What Causes Dark Spots And Discolouration In Scrotum?

i have dark spots of discoloration and a dark line stretching from my scrotum up to nearly the head of my penis. there is no pain or itching, and it has been there for nearly 3 yrs. occasionally i will have pimples pop up as well. i got married over a year ago and my wife has regular VD tests at her OB/GYN and always comes up disease free. is this normal for a 37yr old male or should i be concerned?