Here's what I came up with:
Fold-up Color Sorting Mat with Pocket
I found fat quarters in the basic colors and cut 6" squares of each of the 10 colors. I sandwiched in a layer of felt between the muslin backing to give it a little more structure, and added a simple side pocket and ribbon closure.
It folds and ties for easy storing and carrying.
Mr. One had a good time sorting beads on our new mat.
My boys had fun sorting our tub of frogs and turtles using the mat as well.
Have fun sorting!