I work out fairly hard and as a result, I'm usually soaked with sweat afterwards. It's not always convenient to do laundry afterwards so sometimes dirty gym clothes might sit for a couple days. I noticed that often times, lighter materials (white towel, gray shirt..) get these weird purple discolorations on them...similar to a bad bleach accident or something. It's gotta be my sweat, but any idea why this is? What the heck am I sweating out that it almost dyes material? It doesn't really wash out either.