It is typically blue with thin white shoulder straps, a white single vertical stripe on each side, and a presumptive tail hole as well as leg openings that stop all the way at mid thigh rather than at or near the groin folds (somewhat shorts-type). Usually depicted as a shorts and camisole set, although one-piece depictions are not uncommon.
Even if tagged as such in Pixiv and other sources, please do not add this tag on any posts of horse girls obviously wearing any other competition school swimsuit, or any other swimsuit for that matter. In fact, the 水着ウマ娘 (Mizugi Umamusume) tag in Pixiv refers to any swimsuit-clad horse girl in general, not necessarily one wearing this swimsuit.
