Interesting discussion.
I have very little useful to offer to help you, @MoiraRoseIsMyQueen, as I'm rubbish at answering questions like that too!
I do know that the concept of "race" has been "debunked" by critical race theory BUT it cannot be denied that there are evolutionary differences between people of different ethnic backgrounds (yes, I know, that's probably the wrong word to use as well).
I come from a background in blood science, and it's unhelpful to deny any racial differences and say it's purely a societal construct - because yes, there ARE differences in blood science between ethnicities. Largely evolutionary, as I said, but they're there. There are certain categories of blood type that occur with much higher frequency in black African populations, for example. Certain antigens, both on red blood cells and on other tissues, that are far more prevalent in different ethnicities. One of the problems that rears its head relatively frequently is that it is harder to find bone marrow matches for black patients, and even sometimes matched blood, because of these rarer antigens/combinations and because there are fewer donors from the matching populations.
It's the same for some enzyme deficiencies and some blood disorders too. And of course it's not just black populations, that was just an example.
So in evolutionary terms, I believe it is rather simplistic to deny racial differences between different populations; but in terms of racISM, I agree that it is totally a societal construct that implies that any one population is in any way inferior to another, and is utterly wrong.
I also disagree that you shouldn't comment on skin colour - "colour blindness" is not an appropriate forward move. Acknowledging the athletes' skin colour is not rude, it is factual - so long as no derogatory comments are attached to that.
I'd probably go for the general cop out of "they have black skin because their ancestors came from very hot countries and they had more melanin in their skin, because it helps keep it safe from the sunlight". If pushed and asked why they were the fastest runners, I'd probably go for the other general cop out of "they trained very hard and won the top places in their country" and comment on their individual physique to explain why that would help with their running abilities.