Melatonin due to different sun exposure, that is all skin color is. Once you understand that, I don't see any reason to consider it any more than I pay attention to the callused fingertips of a guitarist.
Cultures are different everywhere, varying across families too. Have you seen how differently everybody raises their kids? That we are used to.
Now there is an argument that what happens if someone's culture is violence, in that case I think it's a legal issue and the legal system can deal with that.
I don't know what else you want to learn. Focusing on these things is not as useful as focusing on increasing the size of the pie, making scientific education as well as the dissemination of scientific news (which has historic low amounts of trust now in the general populace) better and just making the world a better place for HUMANS and other sentient beings. It's really not that hard.
racism is an issue though, and there does need to be a focus on eliminating it. you are right that skin color should not matter, and for some of us it really doesn't. but for others it does. and we need to fix that. it's not enough to explain the problem away. active steps need to be taken to help everyone learn how to overcome it.
there should be no racial bias coming from evolution because mixing of of people of different skin colors is a very recent phenomenon in terms of human history. i believe evolutions influence takes longer than that to work.
and culture? if you grow up in an open community with open minded parents, that's all you need to not learn to judge people by their color. it's as simple as that.
if you didn't have that privilege, then it helps to seek out friends from various colors and backgrounds and let that help you open your mind.
my grandmother grew up with racial bias, and she occasionally expressed that, yet whenever me or one of my cousins brought over an african friend, she loved them, and i hope that one by one it made her realize that her prejudice was based on ignorance.
