Happens right in their hands!
Show your spectator a small rod with some different color beads on it.
Also show your spectator a tin full of DIFFERENT COLOR beads.
Let your spectator choose a bead on the rod.
Dump the beads from the tin into your spectator's hand.
All of the beads in his hand are the SAME color- the color he chose!
Very easy to do!
WARNING: CHOKING HAZARD. Do not put the beads in your mouth. Not suitable for children under 5 years of age.