When buying leotards, two key questions are:
At some studios, only black leotards are permitted. It may even be a specific brand and style of black leotard. If there is a required color, it's very unusual for the color to be anything but black.
Instead, the studio may simply require a solid color leotard. Blue and green are both popular. The solid color should be reasonable. It shouldn't be the same color as your tights!