Now, if the color is too dark, what will you lighten it with? White? Wait a minute. Think. Will white take away the richness of it? White always grays and flattens the color. Don't put it into a warm, rich color unless it belongs there. Then only as much as is needed.
Treat all your tints this way. Is it a high value on a forehead in full light? White first, then a little modifying color, yellow first, then red; perhaps no red: the kind of yellow may do it. When you have a rich color to mix, get it as strong as you can first. Then gray it as much as you need to, never the reverse. But when you want a delicate color, make it delicate first, and then strengthen it cautiously.
These seem but common-sense. Hardly necessary to take the trouble to write it down? But common-sense is not always attributed to artists, and the beginner does not seem able always to apply his common-sense to his painting at first. To say it to him opens his eyes. Best be on the safe side.
=Crude Color.=--The beginner is sure to get crude color, either from lack of perception of color qualities, or inability to mix the tints he knows he wants. In the latter case crude color either comes from too few colors in the mixture, or from inharmonious colors brought together, which is only another form of the same, for an added complementary would make it right. For instance, Prussian blue and chrome yellow mixed will make a powerful green which you could hardly put anywhere--a strong, crude green. Well, what is the complementary? Red? And what does a complementary do to a color? Neutralizes, grays. Then add a very little red, enough to gray the green, not enough to kill its quality.
Or if you don't want the color that makes, take a little reddish yellow, ochre say, and possibly a little reddish blue, new blue or ultramarine; add these, and see how it grays it and still keeps the same kind of green. This is the principle in extreme. Still, the best way would be not to try to make a green of Prussian blue and chrome yellow. It is better to know the qualities of each tube color on your palette. Know which two colors mix to make a crude color, and which will be gray, more or less, without a third.
=Muddy Color.=--Dirty or muddy color comes from lack of this last. You do not know how your colors are going to affect each other. You mix, and the color looks right on the palette, but on the canvas it is not right. You mix again and put it on the canvas; it mixes with the first tint and you get--mud. Why? Both wrong. Scrape the whole thing off. With a clean spot of canvas mix a fresh color. Put it on frankly and freshly and let it alone--don't dabble it. The chances are it will be at least fresh, clean color.