AB is a top coating that has an iridescent almost rainbow like sparkle that mimics the northern lights or the "Aurora Borealis" which is where the name comes from. You will see many rhinestones colors have an AB counterpart such as light pink and then its counterpart: light pink AB. The AB coating does change the colors of the stones but gives a much different look that so many love so be sure to check your color charts and/or product listings for the color of the particular stone.