Tomorrow, I begin teaching a class at my local art center about understanding and learning to see color. One of the most valuable reference texts for this class is "Vision and Art The Biology of Seeing" by Margaret Livingston. This class has experienced adult painters through middle school beginning artists. Therefore, there are advanced and beginning exercises.
Here is an example of an exercise about luminance. Mine is quickly painted and not perfect. However, it illustrates that artists can alter the luminance of an object by shading its background. This center circle is one single shade of grey. The gradation of the greys in the background makes the center circle appear brighter or darker at its edges. This exercise is taken from Livingston's book and is after Shapley 1965.