What Causes Purple Spot On The Foreskin Of Penis?

yes i am a male 20 years of age and i have a had what i would say a deep purple 1 inch long spot on my foreskin on the bottom near the head...for what seems at least 5 years...no pain no itch no change..could this a result of over masturbation or too much intercourse...just really wanna figure it out.. any advice will be appreciated