I've developed an algebraic system for creating a variety of colors for polymer and modeling clay. It's similar to the technique for mixing food coloring. What I do after conditioning the clay (I use the colors red, blue, yellow, black, and white) is form balls about 1 cm. in diameter for each color, making sure to put the unused balls in an air-tight container. I then combine the colored balls using my system. For example 4B+4R means combining 4 blue balls with 4 red balls, 2Y+6R means combining 2 yellow and 6 red balls and so forth. It's much cheaper than buying pre-mixed colors and a lot more fun.
By Angela from Sault Ste Marie, ON, Canada