Semen is the fluid that comes out from the end of a man's penis when he has an orgasm (the height of sexual excitement) and ejaculates. It is usually white, but may also be slightly grey or yellow. If there is blood in the semen, it can look pink or reddish. This is a condition called hematospermia, and may be because of some blockage, inflammation, infection or injury to some part of the male sex organs, such as the urethra, epididymis, prostate or testicles. A doctor should be seen if the pink or reddish colour does not go away after a few days.