We are really big into color sorting at our house right now. Drew really loves to play with these little transportation counters we have and loves to sort them by color. He even tries to "trick" us by putting a color in the wrong cup and waits to see if we will notice. Then he laughs hysterically...which is adorable.
We have several different cups floating around our house and I also made the cups on the right side of the picture using leftover Tupperware and some paint.
And you don't have to have any particular type of object or counter to make this work for you. Just gather up some of your little ones toys in the corresponding colors.