My hubby is the fabric picker. :) I'll show him the quilt design I want to do, the colors I have in mind, and he'll go with me to Joann's and look at the colors and pull one out and ask me about it. Most of the time, if not all the time, I agree with his picks!
One project I was working with all blues and he put them all against each other to make sure there was enough difference in them for my quilt.