Could have a UTI, maybe gallstones or something
he need to go to the dr. starting with std testing. that would be the easiest answer. if he does not have an std then they will have to do futher testing. i found this statement on a web site i hope it helps..
Semen is usually white or grey, but can occasionally appear yellowish. Pink or red semen suggests that blood is present. Although this is only rarely due to a serious health problem, men with semen that seems bloodstained should seek advice from their family doctor