On the Rocks is a vibrant purple-blue with a blue iridescence. The finish is mostly matte, aside from the subtle iridesent shimmer. It’s a pretty spectacular color–I don’t really have anything like it that I can think of. MAC Cobalt is darker, bluer, which is the same issue with MAC Royale–so much darker, much bluer. The texture of this shade was silky soft, and it applied smoothly, evenly, and had good color payoff.