This might be way too much information but I figured I would share it with you just because it might ease your mind.
I'm always examining my boyfriends penis (I don't even know why but usually after we've had intercourse I'll just examine it) and I always laugh because I always find little dots or discolouration's and one time I thought I even saw a pimple (but really it was just a small white speck that was nothing at all).
It's funny because I'm such a hypochondriac and he isn't at all so whenever I mention these things to him he'll laugh and say "oh great, guess I'm dying now - should I go to the hospital"? Pretty much just to mock me because that's the kind of stuff I say to him on a regular basis.
I know I'm a girl so maybe my opinion on this particular topic isn't as relative or comforting as a males opinion but from what I see on my boyfriends there is always small specks of discolouration or even freckles or just different looking spots of skin. It's totally normal and I know that you're fine - you definitely don't need to see a doctor!
Stop concentrating on it too much and do something to help take your mind off of it, you're fine