If clay stains are a bother, think about wearing only colored tennis clothing when you play on clay (not white and with few white accents). They're pretty much permanent stains, because I don't think bleaching is much of a solution when bleach strains the fabric integrity of the garment as a whole. That said, if you wear navy or black or royal blue clothes, the stains are much, much less noticeable if at all.
Agree with the above posters, too. Look around at your local courts and you'll see that the most stained players are the better, more avid players, including the instructors. If they ever cared, they've gotten past the hump of worrying about it and just worry about their games.