Semen under a blacklight?

the unidentified dried stain under investigation is on a thin piece of cardboard. the unidentified stain is dried and left a mark on the cardboard. i have taken a blacklight to it and it showed up a light pinkish purple maybe a very light orange color. not white or yellow. i sprayed hairspray on half of it seeing if it will turn up black...it does not (was a tip from someone).still dont know if its semen. anyone with anymore knowledge or experence in this area will be much appreciated.