What Causes Weird Spot At The Base Of Penis?

Hello , i have a little different color spot on the base of my penis, i havent had sexual intercourse recently but i did notice it the morning after i masturbated before sleep. Its very strange to see this, first time ever. What is it? Im healthy 21 years old i don t understand it. It doesn t itch nor it is bumpy just a spot on the skin. Please help me know