You could probably find photographs on the Internet to show a normal penis with foreskin retracted, and could see if it looks like what you're finding. Vitiligo comes to mind, but usually white skin in vitiligo is patchy, not even. There's a white substance called smegma that can accumulate under the foreskin, but that can be washed off. It might just be normal pigmentation, which is why I suggested you try some online health pages and look for a normal penis with retracted foreskin.
If you do decide to talk to a doctor, you could ask for a urologist.
Upload pictures on a link if possible