Someone who is technically oriented and persistent; with a desire to get an understanding of the lower structures of the operating system, would be a great candidate for Gentoo. Regardless their familiarity with Linux.
And Windows isn't telling them. That's part of the issue. If Cortana could tell them "this boot was slow because your video driver missed an update necessary for other system packages. Would you like me to show you how to fix that now?" that would be a win for your typical user.
My nextcloud calendar doesn't seem to have a category color, only color per sync account. I'll look to see if there's a plug-in, as I'm somewhat interested as well.
I would bet there's also a bug report somewhere with such a request.
I won't be able to test iOS easily (the rest of the family have them, but they don't release them easily).
Not OP, but great question. A lot of discourse seems to imply that we should already know.
Historically, there were groups that identified that way for very specific reasons (against European monarchy in Central America for instance).
In the US, at least, these concepts are quite loosely defined, and I'd even argue, undefined.