Humans are not "basically the same" but humans are also not easily divided into a couple of genetically separate races. Many black Americans, for example, have white ancestors. And black Africans are genetically far more diverse than the entire rest of mankind put together. There are people with every possible skin colour between black and white. Our insistence on drawing a handful of arbitrary lines between them is cultural, and not based on a clear genetic separation.

That said, skin colour does have some physiological impact: darker skin blocks the impact of the sun on our skin, which is great for preventing sunburn (and skin cancer, I think?), but reduces the amount of vitamin D our skin creates, and vitamin D deficiency can have an impact on all sorts of things (no idea if glaucoma is one of them). That makes it a trait, though, not a race.