I've always been drawn to the paint strips at the hardware store, which is why I was so happy to see this color matching game at Chasing Cheerios which uses them.
Variety of paint strips (be sure to get two of each color)
Hot glue or double sided tape
-Cut one set of stips into small rectangles a little larger than the head of the clothespin
-Attach rectangles to clothespin using hot glue or double sided tape (thanks for the tip, Julie)
You may need to demonstrate how to open a clothespin or assist your child the first few times (you'll be surprised at how quickly they'll pick it up, though). This is a very easy way to talk about and identify colors and the varying shades of each color. Even better for helping with dexterity of small fingers and hands.
For those children who can easily match the varying shades of each color, it's fun to teach them the fun paint names (mystical grape, magenta, calypso orange) that are printed on the strips.
If your child is more interested in opening the clothespins than matching colors - another option is to give them a can or small basket to put the clothespins on (Thanks for the tip, Maren).
We usually start this game by placing all of the clothespins inside the can - draw each out one at a time and say the color as we are placing it on the can.