Why are people racist to towards other skin types?
Probably because a long time ago, the other ‘skin types’ were more ‘primitive’ than the others, or more ‘barbaric’ and savage’, and so on, and so they considered themselves better than them, and made them slaves, and people, somehow still believe that others are less than them, mainly because they grew up hearing this said by their parents, and their grandparents.
I suspect it has very little if anything to do with skin tone. In my opinion “racism/ist” is an essentially meaningless, if somewhat ironic term which ethnic bigots (supremacists) and commie-fascists like to use when they want to force their irrational beliefs on normal, more emotionally balanced people. The term is typically used in conjuction with implied or outright threats of violence, particularly against White traditionalists.