There are a lot of parents who are really into gender-indifference, so unless you know that this is simply a hand-me-down situation, be careful how you approach the parents. You don't want to offend or (maybe worse) get a lecture on why it shouldn't matter whether the kid plays with Barbie or GI Joe. (just kidding...sort of...)
I had one absolutely adorable little boy in Parent & Me who wore white skates very proudly. He won them in a raffle - his first time ever winning anything! His parents didn't make a big deal out of the color, so neither did I. I think that, given his self-confidence, he would tell someone who teased him, "They're my own skates, that I won all by myself!" (They were a tad big for him, too, but he was determined to wear them because they were his.)
If your student is doing okay on these skates, you could share that with the mom. Something like "He's doing really well on those skates- you were smart to reuse them." Suggest changing the laces since they might be a bit stretched out or worn. If she brings up the color, then you could offer suggestions on turning them black. (I think a checkerboard pattern would be cooler, though, lol.) If she doesn't mention it, I'd be color-blind. After all, it really doesn't matter as long as he can use them.
We don't have any other boys at our rink wearing white skates, afaik.