My boyfriends penis turned black and blue under the head of it last night after sex. there is swelling but no pain. it looks like blood blisters ?

Rupturing vein?: The described scenario very likely represents the occurrence of rupturing superficial penile vein with local blood infiltration leading to ecchymosis-black & blue, which will extend its involvement & fade its color in 1-2 wks, and leave no consequential harm but with possible recurrence - though rare. If hurting with a node at the center of ..., unwanted penile curvature may appear. More? Ask Dr.