Or can they have pale skin as well?

All in-game examples of Redguards have had what we'd describe as "African" features in real-world talk.

Some are lighter or darker than others. The same is true of any race in Tamriel. There are Imperials and Bretons with much darker skin than others.

Maybe albino redguards?

Are all Dunmer grey?

Owyn is red. A red Redguard.

They look red to me

No, they aren't all black.

Perhaps as importantly, it wasn't funny. Coulda at least made sure it was amusing.

No, not all Redguards are 'black,' in part because 'black' is a horribly inaccurate term for a whole range of skin tones, but also because Yokuda was a huge continent and because TES races are as much a socioreligious thing as they are a biological one. They are all darker skinned, though, I'd wager; ethnic looking, for lack of a better term.

All iteration of Redguards, save for OB, have had varying shades of brown, from pretty dark to moderately brown. Oblivion is special, in that it was the only one to make them varying shades of red and reddish-brown (with green lips o_O )

I'd say there all black, not skin tone but ethnically? not sure how to say that. I think they were red with green lips because of how the tint/tone system worked for skin colors in ob. If you look at all the redguards in morrowind they had darker skin, not some weird red with green lips thing going on

Not all of the redguards in ob were redish either so idk if it was a design thing or what

Redguards range from light brown to so black it's almost blue, all with a twinge of red. I think it's said in one of those guides to Imperial Tamriel.

Why are they dark-skinned? What properties inherent to Yokuda necessitated that they have dark skin? Apparently altitude and climate doesn't have much effect on Tamrielic races. Was there some Aedric/Daedric intervention involved?

They're the offspring of black locust gods.

One of the Lessons states that Vivec went to Yokuda and fathered a race or sub-race. This could be literal, metaphor, or an out-right lie. Other than that we don't really know. Vivecs gonna Vivec.

Source?I'd imagine its possible for an ordinary human in TES to get a tan so I doubt its that far fetched for a race of humans to adapt to hot weather.The Nords are rather pale skinned and tall which makes sence since they are in a cold climate.The wood elves are small,which could be an adaption for them so they can easily get around forests.These may be adaption,but I see no reason why altitude and climate wouldn't have an effect on the non-beast races.

Just to add,you could create a white redguard if you messed with the skin tone at the character creation,but I'd take this with a pinch of salt as you could create a black/red high elf and a luminous blue-y argonian,which I haven't heard about in lore.

I have heard they are supposed to be like the real world equivalent of Africans with a red tinge to their skin.