What Causes Discoloration In The Outer Vagina With White Patches On Thumb?

Hello. I have discoloration in the outside of my vaigina (hood of the clitoris) along with small white patches on my thumbs only. I consulted a dermatologist along with my physican and they both said it looks like vitilago. But bot quite sure, they ran a bunch of test and hormone test and everything came back negative and normal. What could this be?