What Causes White Patch On Shaft With Negative STDs?

hello im 18 years old, my name is adam. i havent had sex in a long while, and i have been checked for STD's and it came back negative. i get checked every 6 months, but lately theres been this patch of white skin on my shaft, almost like a drop of bleach fell on it. it doesnt hurt doesnt itch, doesnt peel or blister or nething its just white skin thats discolored compared to rest of my genitalea. theres only 1 and im circumsized. ive looked all over and i saw vitiligo but it says thats very rare, so i wanted to know if there was something else this could be other than that? as i said ive been tested no stds.