The beauty of grays
First of all, grayed colors (or tinted grays) have all the properties of colors. They can be used with any other color (besides neutral gray) and participate in color interaction without causing problems.
Often, it’s impossible to 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 light and atmosphere often work towards desaturation. Atmospheric haze makes colors bluer and less saturated. Twilight makes colors darker, bluer and less saturated. The bright noon sun makes colors dazzlingly brighter, and, once again, less saturated. The effect of a partial solar eclipse is pure desaturation of all colors. In fact, in most lighting conditions, you can see the proper, clear color only at the edges of the highlights, but not in the highlights or shadows. These effects 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 results. 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 grays successfully, one must remember that the less saturated the color is, the less influence it exerts, 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. A 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 chromatic tones as grays near them as well! Next to a pure spectral color, even a well-tinted gray can still resemble 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.
