Color-safe shampoos run the gamut, but all of them will get the job done. Here's what's important to remember: for pastel-haired people, a purple shampoo is a good option to balance the brassiness in the blond showing through under the light color. The darker the purple, the more potent it will be on hair, thus really counteracting that brass. For those with darker-colored rainbow shades, any color-safe, sulfate-free formula will do. Those will be the most gentle on colored hair.
Lush Daddy-O Purple Shampoo ($12 and up)