6mm rigging beads are needed when making a Carolina Rig (sinker, bead, swivel, leader and hook). The bead is used between the sinker and swivel to keep sand from filling the sinker and breaking your line.
Colors: I like to use a clear bead in the summer or whenever corbina are present. In winter months (Nov-April) I like to use various bright colors which help to entice massive perch and croaker to bite.