Rav Shteinman responded, “So if there’s no difference, why doesn’t he just wear the black one?”
That’s not an answer, that’s a dismissal.
There are plenty of reasons why he might want to wear the other yarmulke. Perhaps he likes the color better. Perhaps it stays on his head better. Perhaps it feels more comfortable for him. Perhaps it has sentimental value for him (it was made/given to him by someone who means a lot to him).
The Wolf