Hi Pete, rust colored stains could mean dried blood. It could be a sign of infection so it would be a good idea to see your doctor to have him check it out.
Hi ,
Nipple discharge is always an abnormal finding in men and should be taken seriously.
It could be that you have an irritation caused by your clothing rubbing against it while you are exercising and sweating.In adolescence,nipple discharge is normal but a discharge in adult men should be followed up with some type of testing to rule out a more serious problem.
Please do consult your doctor.
Take care!