I've never been a fan of the colors.. but I've said that since you've ''bought'' them.. you should keep them.
So you spend points on a color, then spend points on another color, you can just select which one you want in a drop down menu.
Especially if you have gradients..
People some times buy 1 color and keep that because it would be a waste to buy another.
But if you can buy them all, it would take the points out of the game and allow people more choices.