OK

Watching, "Eye of the Beholder: The Art of Dungeons and Dragons," and there's a section on inclusion.

OK.

Fantasy settings are myth parallels of Europe for the most part.

You want to play a character who has dark brown skin, because you have dark brown skin and you want a character that looks like you.

Thag Grok.  Though Thag always thought the idea was to play someone who isn't you.

But let's unwrap this.

There's black people in Europe right now.  There's black people in America right now.

There weren't in medieval and renaissance Europe unless they'd been dragged there to be an oddity.  They didn't have communities there.

Europe wasn't sexually egalitarian either, and most D&D games are.

Well, there's a reason that we don't see more black people in historical Europe.  They aren't from there.

A white person in sub-Saharan Africa is also pretty damned unusual.

So, how did they end up everywhere?

Well, for America, it's slavery.  Spain and England dragged them from Africa and dropped them here to work for considerably less than minimum wage.

Considering that a medieval or renaissance Europeanesque society might possibly still have slaves, that's probably not a good explanation for their presence.

First, your world will need a place where people with darker skin evolved.  I tend to keep the reasons for darker skin the same as history.  More sun more often.  That will be a different place from where white people evolved, less sun less often means less melanin.  There's lots of real reasons for skin color developing.

Next we need a reason there's black people in our Europe analog (or white people in our Africa analog).

Well, most fantasy settings have something that Europe and Africa sure as heck lacked.

Magic.

It allows for much faster travel than state of the art walking or riding.  That allows for faster communication.

That magic doesn't require a technological base that means the place where the darker skins evolved can, reasonably, be expected to be on par with the white people when they encounter each other.

Faster and farther communication and trade means that people will travel between the two regions and magic also prevents the mass transmission of plagues!

So, there's no reason your elf can't be black.

There should be a reason they are is all.

It's your world you're making from whole cloth, you can even have the reason be so far in the past that the cultural differences between the black elf's home culture and the culture of the setting no longer matter.  The reason for their migration doesn't even have to be happy, the Irish sure didn't get a happy first few years in America!

Also, it's your world, you don't have to have racism unless you want it.  I tend to skip it.  When you have Orcs and genuinely evil mages who can summon the literal denizens of Hell, differences in skin color starts to matter a lot less.

But, remember that reason for there being black elves?  It works best if that reason is there from the beginning.  If there weren't black elves in the setting for, literally, decades your explanation had better fucking ROCK.

That's why my fantasy setting having black elves doesn't raise an eye and there suddenly being black characters in Lord of the Rings causes outcry.  Especially since there's no explanation even hinted at.