I wash mine at least once, usually twice, a week, but I have gray sweat stains around the collar and the cuffs, a gray dirt stain across the upper back from rolling around on the mat, and a yellow and orange stain across the waist from cheap dyed belts bleeding color. And they just won't go away. It's not a big deal, but it's annoying. I've tried oxyclean, clorox, clorox 2, everything I can think of. I don't want to drop another $60+ on a new one when there's nothing really wrong other than the discoloration, so I'd be grateful for any advice.