I believe it was because his current form is similar to that of a corpse, while alive, it cannot change the fact that he's rotting with the passing of time(I think?)... Or at least someone taking the form filled with despair, loneliness, everything negative, like that. After all, he too, believed his current form is monstrous.
But do not fret, because I too, was shocked and dubious that he's white hahaha
well there's also the thing he mentioned the artifact that helped him make a proper humanoid form as he doesn't want to reveal his real form becuz he considered it as a monstrous
but decaying doesn’t turn you black, it just removes the pinks and all the color undertones. so this doesn’t make sense + feels quite racist that they believe the form of monstrosity is somehow dark skinned
I found it a bit strange that his “handsome” form was white and blonde while his “ugly” form was dark skinned