When creating a realistic drawing, being able to see the true value of color is just as important as observing how light direction makes shadows fall. Value is the degree of lightness or darkness of color and certain colors can fool the eye. For instance, if you put a swatch of red and a swatch of green side by side and each were the same value; the red would look brighter
Here is a good exercise for learning to see color as value. Use your pencil to make a swatch of any solid value at the edge of a piece of paper and then hold the paper up, squint your eyes, and find a color that it matches in value. It’s important to make your practice swatches along the edge of your paper so you can hold the paper up and see the swatch next to a color. Next, pick out a color and try to match its value in a swatch near the edge, hold the paper up, squint your eyes to check to see how close it is, and then try again if you missed capturing it’s true value.
Carol Rosinski
Toad Hollow Studio – Drawing Lessons and Inspiration