Wait.... What Kaep. is black? The last time I looked. He look like he has some Indian in him or part mexican. But black he is not. He has a tan look to his skin. That is it.
Just so you know, Mexican is not a race. It's a country. Lol.
Black people encompass the whole range of colors and facial features. They're black people in Africa, who have never seen a white person in their life (except Anthropologist, Geneticist and other scientist), who are light/of light complexion, with Chinese eyes and straight noses, who scientist say are the oldest living people on earth (such as in Southern and Central, East Africa). So what you're saying doesn't mean much.
Saying all that: Kaepernick has a black and a white parent. And this is the reason why he was called black by some huddler's. I would call him mixed or a mulatto type myself (unless he has wooly hair, which is hard to tell, cause he keeps it cut so low). But then again, anthropologist would say he has a tropical limb build/skeleton and classify his as black. Nonetheless, there are black people with two black parents that can be of lighter complexion. Just as a black parent and a white parent can still produce a black child (phenotypically), even if their genotype is mixed.
It's not always as simple as you make it. And for the record, Native Americans (I think you called them Indians), can range in complexion as well. However, the one's from Mexico are usually much darker (and shorter for that matter). Lol