ColorMixingTool

Using this software, a color extracted from a photo or from the HSV circle, is analyzed to a compination of three colors (the default colors are: Cyan, Mangenta and Yellow - except Black and White that are fixed). Besides, you can create your own palette of colors.
Vice versa, You can adjust the amount of colors of your own palette and this software finds the resultant final color.
The above functions are very helpfull in painting, while you can reproduce all desired colors from a pallete of three available colors, the black and white.