How many plants does it take to make a garden? Sounds like a good topic for a thesis — in horticulture or philosophy. Among painters, a common creative exercise is to squeeze out a discreet number of colors and from them mix everything they need — a less-is-more strategy. This is not, however, equivalent to a fighter having one hand tied behind his back. Many artists contend that a “limited palette” is the true path to understanding color and achieving a harmonious painting. Witness the mood-setting tones of Rembrandt, Picasso in his Blue Period and Van Gogh’s sunflowers.