i have always been fooled by this too... my neighbor has a pool and his parents told me that pee turns red ..... I of course never had the guts to try it incase it did turn red so i have decided to go pee in his pool!!!
Apparantly my wife was told this as a child too. She believed it up until a yr or two ago - when she was about 24 or so. Its the funniest thing in the world to me now - I will chide her about it to no end when we go swimming. Ill even add in Easter Bunny and Santa Clause referrences - like "dont forget to check in with Santa if you need to use the bathroom." Funny funny stuff.