My boyfriend and I have a lot of sex, and this happens sometimes. Not very often but sometimes I notice that his cum stains yellow. This weekend, we had sex at 3 in the morning. Obviously after that, I was really tired and so I put my underwear back on and went to sleep. When I woke up early the next day, I had noticed that my underwear were still wet from his cum. As I got. up and started my morning, it dried and by the time I looked again, it had dried as a yellow color in my underwear. Is that normal? This. happens once in a while. Is it actually cum? Why does his cum stain yellow sometimes, but not other times? Did it just stain like that because I wore my underwear to. bed with cum in them and it didn't. dry for awhile? What happened here? Did I accidentally piss myself and couldn't tell? Surely I would have felt that right?