While Lincoln Kirstein noted that the unitards did show clearly the dancers' lines, he too found them distracting: "Union-suit tights are hard to make look neat, but the line of undergarments shining through continually destroyed the line."
Source: wiktionary
The unitard consists of a leotard (a sort of stretchy one-piece bathing suit) attached to a pair of tights, which completely cover the legs. The unitard can be worn by anyone — men and women, boys, girls, and extraordinarily graceful household pets.
Source: wiktionary
Backstage (that is, in the high school locker room) before the show, all the other senior girls were pulling on their red unitards for the jazz piece.
Source: wiktionary