When I comment on other people’s work, in particular digital work, one of the most frequent phrases I say is “Do not use neutral gray together with color”.

I have even written an article called “Killer grays” which elaborates somewhat on the subject, but its points remains the same: unless you know exactly what you are doing, don’t use neutral gray together with color. It is too easy to get a neutral gray on computer (fortunately, not as easy with physical media), and its effect when used as if it were any other color is disastrous.

But since knowledge cannot be harmful, and in the light of the nice rule “rules may be broken”, and in the light of “know thy enemy”, and indeed in the light of embracing our enemy, I am going to look at the neutral gray and its cousins in detail, to show exactly why it does not live well with color, what could be done to fix the things, what subtler traps lie beneath the quiet water, and, ultimately, when — and how! — to break the rule.

Science of color

We begin with understanding how color works. Let’s start at solid, measurable, verified facts. Color is a thing between physics and physiology: it is the perception of brightness and frequency spectrum of the light. Both brightness and spectrum of an object depend primarily on the quality of the colored object’s surface, with added influence of the brightness and spectrum of the light itself. The brightness in art is usually called tone or value, and the spectral quality is called hue.

Pure colors have a very narrow spectrum: their brightest part is very close to a single frequency. (Laser light is the extreme, since it is a single frequency.) Due to the nature of color perception, the wider is the frequency range of a color, the grayer that color looks — until its spectrum covers the complete range of visible light and it becomes white. The three kinds of receptors in the eye are tuned to the low frequency end of the range, the middle, and the high frequency end, and their signals are processed by their intensity relative to each other; and so when all three receptors receive the same intensity of light, this is perceived as white of some brightness. In mathematical theory of color, the width of spectrum is linked to the third parameter, the saturation. The closer are the intensities of signal of the three kinds of receptors, the wider the spectrum is, and the less saturated the color is. White is completely unsaturated, and it has no hue since it does not have any peaks at any distinct frequency!

The brightness of the light, on the other hand, is perceived without regard for its frequency, it influences the signal level of the eye receptors directly. No matter how bright the laser light could be, it will never seem white - it will only be very bright pure color. As the brightness decreases, the color gradually descends toward black, which is simply how we perceive the absence of light. The absence of red looks exactly the same as the absence of white! And black also is unsaturated and has no hue, since brightness itself is just the amount of light, and does not depend on its frequency in any way.

So color is really two channels of information, due to the way our eyes are built: frequency information and intensity information, separate. Artists learn that in form of speaking about chromatic and achromatic scales: the chromatic tones carry frequency information (i.e. their spectrum is uneven) and brightness, the achromatic tones carry none, they only have brightness.

Brightness perception is more basic than frequency perception; most animals only see brightness. The spectrograph in our eye is a much later evolutionary acquisition. It could be compared to music, since color is really as mathematical as music (even though it may sound surprising): the brightness is the rhythm, the hue a direct analogue of the scale. Just as musical rhythm provides the basic organization to the ear, the brightness levels organize the visual image. Hue and musical scale only add another dimension: one can make pure-rhythm music on a drum, one can make pure-brightness image with black and white. (I avoid the term “tone” here, because its meaning in music is unfortunately the opposite from its meaning in color science; musical tone is analogue of hue.)

Gray in nature

Colors become progressively gray as their frequency range widens (saturation decreases). At some point, there is so little distinct hue perceived in them that we start calling them all gray; but you can get different grays depending on where we began: there is greenish gray of concrete, and yellowish gray of limestone, and bluish gray of slate, and so on. In fact, most real world objects transmit or reflect a rather wide frequency range, i.e. they all are more or less “gray”. Completely saturated colors are rare. But completely gray objects do not exist.

That’s right, you never see a pure gray in life. Even if you made something that reflects the complete spectrum evenly, it would not be completely gray just because the light is usually colored: the Sun’s “white” is yellowish, the sky light is bluish, so even our hypothetical case would be slightly tinted. If something colored is put next to our pure-gray, the diffuse light reflected off that object would tint our gray. The eye also does tricks with perception of juxtaposed colors: it is a side effect of the neural scheme that enhances contrast, so a color next to red will look greener than the same color next to white, and redder next to green.

Which finally allows us to understand what a neutral gray is. It is just another name for the “colors” of the achromatic scale. It is not, strictly speaking, a color at all, since it lacks one of the two components of color: neither white nor black carry any hue information, and neither do their mixtures. If you add white paint to any color, that would increase its brightness and somewhat widen its frequency range - desaturate it. If you add black, that would decrease the brightness, and also desaturate it. Brightness is the only thing white or black can contribute to a color; frequency information they can only take away, making the frequency range wider and as such less distinct. (Information is always in the differences, a uniform spectrum carries none and is also known as white noise — the name “white” is entirely not coincidental here!) Mixing white and black can only produce pure, colorless brightness. And that interacts with other colors in quite a different way.

Artistic color interaction

The artists use the perceptual qualities of the eye to build color interaction in their pictures, using actual pigments to imitate the contrast-enhanced image that the eye would normally see. There is no light running inside the picture; there are just adjacent color spots. The eye believes it sees a blue shadow not because there is an object whose shadow side only receives the bluish diffuse light of the sky; it just sees the pigment reflecting an appropriate color. Perceptual interaction of the hued spots on a flat surface imitates the effect of real light interaction in the environment. And if some color is not entirely appropriate in the context, the eye — especially a trained artist’s eye! — will tell that the color is “off”.

And so, finally, we are ready to understand the treachery of neutral gray.

All chromatic colors, no matter how grayish they are, always interact with each other’s hue, making their cool neighbor warmer and becoming warmer because of its presence (and vice versa), and they interact with saturation too, grayer colors making adjacent ones seem purer (and vice versa). But anything from the achromatic scale cannot influence the hue of anything, because it does not have any hue, nor saturation, because it has no saturation — and since no actual light is traded in the picture plane, there is nothing to tint it either! It only takes perceptual influence from adjacent colors without giving, and forms a hole in the colored picture. For an artist’s eye, such a hole is as good as a poke in the eye with a sharp stick — it ruins all color interaction near it.

Neutral gray and computer

The only way to make something like that with paints is to mix our whitest white with our blackest black. Real world pigments can’t give us a perfectly even spectrum, but we can get pretty close. (In fact, artists have cautioned against mixing white and black for centuries: it looks bad next to color and if mixed with other pigments, it only makes dirt.) But the computer monitor is an instrument that does not use colored pigments; it is instead built to work with the receptors directly. Its three phosphors radiate three pure, narrow frequency colors that activate the receptors right in the peak of their sensitivity range. The spectrum of monitor’s “white” is not uniform like the real world white, it is three-peaked. But the eye cannot tell the difference. And as such, the monitor (and television screen) is the only widespread device that can make us see the true neutral gray — by stimulating all three kinds of receptors equally.

The outcome is disastrous. The monitor’s neutral gray is much purer than any mixture of real pigments. The “hole” effect is much more vividly evident; it is augmented; it stands out obscenely.

“I can’t see it”

A lot of people claim to not see it. Chances are that you, the reader, also do not see it yet. There are two main reasons for it.

First, people just tend to not see. They “see” by giving names to things their eye perceives, and insist that a sheet of paper is white no matter what color the ambient light is: they perceive the actual color, yes, but they believe it is white even if the lighting makes it deep red. The “artistic eye” I keep mentioning is (in part) the ability to pay attention to the actual color, not to some symbol in the mind. Only if you had ever thought of that, you will be able to understand and thus able to notice an actual color. The only solution to this is learning to see instead of the habit to “see”.

Second, a lot of people use bad or poorly adjusted monitors that do not produce exact hues. On some monitors, neutral gray is rendered decidedly warm or cool. That offsets the perceptual effect... for them. Anyone with a better tuned monitor will experience a poke in the eye. In fact, a badly tuned monitor makes all colors wrong, so the problem is not limited just to neutral gray. There is a whole science and black art of tuning the color of a monitor, usually called calibration, but the general solution is investing in a good monitor if you are going to do serious work on graphics, or nothing you make will ever print or display right.

What to do

If you are working with physical paint, it’s simple. Just never use black and white in the same mixture when working in color. Ultramarine mixed with burnt sienna makes a good base for a variety of non-neutral grays.

If you are working digitally, and are not sure — just avoid colors with their saturation too low (avoid the R,G and B component valuess too close to each other if you do not work in HSV system). At the very least, the saturation must not drop below several percent — and if there are more saturated colors next to it, then even 20 percent may be not enough. Always tint the grays.

Pure black and pure white are found at the edges of both scales, chromatic and achromatic alike, and so they are compatible with both colors and neutral grays — and but only when they are pure and unmixed.

Working en grisaille or in black and white is absolutely no problem in either case, since achromatic tones work with each other perfectly. They only wreak havoc on chromatic tones.

But for both physical pigment and digital color, the ultimate solution is knowing how the gray works, and not just avoiding it, but using it to your advantage. That’s what we shall discuss next.

The beauty of grays

First of all, grayed colors (or tinted grays) have all the rights and abilities of colors. They can be used with any other color (besides neutral gray) and participate in color interaction just fine.

In many tasks you actually cannot avoid using grayed colors, especially if you paint from life or need a particularly realistic painting. Painters whose job is producing pictures that must seamlessly blend with photographic material, like matte painters working in cinema, practically always use a very subdued, grayed palette. Most natural colors are not pure; many are quite desaturated; and the light and atmosphere often works toward desaturation of color. The atmospheric haze makes colors bluer and less saturated. The twilight makes colors darker, bluer and less saturated. The bright noon sunlight makes colors dazzlingly brighter and less saturated where it falls. The effect of a partial solar eclipse is pure desaturation of all colors. In fact, in most lighting conditions you can see the more or less proper, clear color only at the edges of the highlights, but not in the highlights or shadows. All that can and should be reproduced when painting. Grayed colors can also be used together to a beautiful subtle effect. I have seen some excellent artists working essentially in two tones, cool gray and warm gray, with great result. But they can be used in full color compositions too, and, since a lot of things are gray or grayish in color, you can’t avoid using them.

Avoiding neutralization

To use the grays successfully, one must remember that the less saturated the color is, the less influence it effects and the more influence it receives. A more saturated color will always influence a less saturated one much more visibly than the other way. This is called neutralization. Some color that could be used as gray in one composition, could be used as a full color in another.

If your composition has strong, saturated colors, then you have to use stronger, more colored tones as grays near them as well! Next to a pure spectral color even a well-tinted gray can still look a perfect hole. This is a thing to avoid, just as if it were a true neutral gray, because the final effect could be just the same.

Working en grisaille

Working in a range of tones of the same hue is called working en grisaille. To qualify for the title, the image must use a range of tones: line art does not. It means painting with tone only.

Per se, it is a valuable style of monochromatic art, and is often used in preparation to painting in color, since it can establish the tonal composition of the image without the color. I mention it here only because a lot of amateur (and even professional) artists make a mistake with it very similar to using neutral gray in color work: they “color” different parts of the picture with monochromatic ranges of a single hue each, every spot essentially its own en grisaille patch.

This kills the color interaction in the picture as surely as adding neutral gray to it. A single monochromatic range works because that’s how our night vision works. But we subliminally expect the shadows be of different color than the lit parts of any object, the red cube to throw its rosy radiosity on a white wall, and so on. Working in this “compartmentalized grisaille” simply does not imitate the natural color even remotely, and so looks dull and false.

This error is especially widely spread among artists working mostly with computer, and can be attributed to the particular vicious style of making light and shadows propagated by many Photoshop users and even teachers. Instead of working with color properly, they quickly fill the different parts of the image with flat color, and then add “highlights” and “shadows” in two separate layers set to Screen and Multiply mode with pure black and pure white. Neither changes the hue in any way, altering only brightness, and the resulting image is an instant “compartmentalized grisaille”. This vicious practice is even more widely spread than just using neutral gray in color work, and while only the freshest newbies do this mistake with natural media, I have seen many digital artists doing it, who were otherwise considerably skilled. The only remedy for it can be studying color theory and learning to see color. Even an amateur artist with no big skill at seeing hues would benefit greatly from merely applying the rule of complements, making the shadows the opposite hue of the light — which is roughly how it works in real life. “Fake it until you make it” — keeping trying does develop the ability to see true color.

Uses for neutral gray

And finally, I am going to give some tribute to the dreadful, abusive neutral gray. Just as many poisons can become medicines in smaller dose, neutral gray has its uses.

First of all, the neutral gray is invaluable in digital art because of... user interfaces! While it does disrupt color compositions when inside them, it also frames them without affecting their hue, which is a very valuable quality. A colored window frame would inevitably interact with its contents, a red frame making the picture greenish, for example. Neutral gray is the only color (besides black and white) that does not have this quality, and so if you look at the working area of Photoshop or Painter, you’ll see it is neutral gray regardless of what fancy “skin” your interface might be using.

Second, a mixture of black and white could be used as underpainting for glazes, to achieve the translucent effect in oils. However, it's not the only way to do so, and thus not special for neutral grays. Third, the clash between colorless neutral gray and color is really a particular case of contrast, and contrasts are what makes compositions work. Granted, it is the most unnoticed and viciously used contrast which is unwelcome in overwhelming majority of cases. But an artist knowing what he is doing could use that contrast almost just as any other to the benefit of the composition. Almost, because it is so universally abused. The easiest way to put it to use is having just one small element in an en grisaille picture in bright, vivid color — it’s an instant attention device. Making the monochromatic picture in neutral gray (indeed, making it just in plain graphite pencil) would only enhance such contrast, by bringing the saturation contrast to its extreme— and it will not form a hole, because in this case the gray will provide the environment.

Neutral gray could also work if all other colors are very desaturated themselves, where the interaction is already very low and subdued and can’t be disrupted as badly. In such environment, if used with caution, it could work as a color: if the overall tone is warm, it could serve as cool tone, and vice versa.

In general, a spot of color feels better in colorless environment than colorless spot in a colored one, though. I have not seen a single case of the opposite - all cases of a neutral (or just too desaturated) gray in a distinctly colored picture instantly punches an ugly, conspicuous hole. Any color must be used carefully and with awareness of its interaction with the composition, but neutral gray requires extra wariness.

Until you are skilled and confident enough, I’d still advise to leave it alone, though. A skilled chemist can work with poison without adverse effects... but I don’t think anyone without proper training should handle potassium cyanide.