I have darkness of the skin on the scrotum. I notice a ex partner had a dark vulva and when I gave her oral stimulation the first time we were intimate and it made her skin a bright and healthy colour the next day. I though maybe she might of had a designer vagina (operation) and that I had awoken up the nerve endings through stimulation, as she told me she had no STD's or STI's. I have since noticed that I have now got a darkening of the scrotal skin, but when Im happy or they are warm in the shower it goes back to the normal colour. I have had 2 full sexual health checks with have I have not heard back from my local clinic, so that means im all clear. Does anyone have any ideas as researching this online is not working lol. Thank you?