I’m still confused about the difference between a background character existing with vitiligo and tokenism
Tokenism is defined as "the practice of making only a perfunctory or symbolic effort to do a particular thing, especially by recruiting a small number of people from underrepresented groups in order to give the appearance of sexual or racial equality within a workforce."
the difference I would say is the approach and way that the author frames the character(s)
a background character withi vitiligo is a person who exists and happens to have vitiligo
a token character is a background character that exists fully for the intent of showcasing that there is a disabled character at least somewhere in the story even if they're there for a split second.
With vitiligo tokenism could also play a role in colorism as well as its a disorder involving pigmentation loss. So a token character of color might have vitiligo to subconsciously make them whiter.
Intent, research, and understanding of the specific group of people being portrayed are what really highlight the difference between the two.