Value is the single-most important element of painting, more important than color, line, perspective or anything else. The Impressionists were well aware of this and often substituted wildly different colors that are the same value. They got their reputations by playing "loose and fast" with color, which was scandalous to the realist painters of their time. If you look at Monet's "Water Lilies" for example, you will see many colors not found in natural water lilies like purples, blues, reds, etc.
When you treat color as value, you can substitute any color; even unnatural and high-intensity colors, as long as they are the correct value. This is the concept behind some of the most colorful and successful paintings. For example, here's a painting of a pelican in naturalistic color, and one substituting high-intensity colors for the same values.
The two look like pelicans, but the wildly colorful version is more appealing, at least to me. I'm a nut about color, and I'm betting you are as well, or you wouldn't be interested in reading an artist's blog. If you want to try this for yourself, you are welcome to use my formula:
As you can see in this chart, you can choose any color for a 5 (dark) value and substitute it for black. Better yet, any middle value (3) color can be substituted for another like orange for blue, or red for green. This creates a Warhol-effect giving your paintings brilliance and intensity. Here's a good example of color as value...
If you want to try this, but don't feel comfortable doing it on your own, join me for "Painting Shorebirds" classes coming up at Beach Art Center Dec. 3, 10 & 17. For this class, you will start off with a presketched canvas (line drawing of an egret, pelican, and sandpipers) and work from dark-to-light with me, substituting colors according to values. It's great fun, and will make you see color much differently and use it more appropriately in all your work.
Here's another example as a pet portrait. I teach pet portrait workshops as well. This one happens Fri. Feb. 28 from 6-9pm at Beach Art Center.