I'm so sorry none of us has gotten back to you yet! WELCOME
and bless you for saving this little guy!
Funny you asked this, bc I just went to the vet w/ my Wylie bc he had some little brown "spots" on his outer manhood area - and she said it was totally nothing. He doesn't have discolored skin, per se, but he does have the spots. But, I don't think what you're describing sounds too abnormal from what I've heard. Could you post a picture maybe?