I'm not sure why it didn't occur to me before. But I'm wondering now if UU/uu is a failed clone (or two). There seems to be hints that they have a mutant blood colour like Karkat (and the Signless before him). Which by the Condesce's view would immediately make them failures. But maybe not worth immediately killing. Maybe something to be studied to see where things went wrong.
........of course, if they are a split personality, would it be possible to have a shifting blood colour? I mean, if not I'd say they're probably a lime green since it's the one (mutant) colour that Hussie has said exists that hasn't come up yet and has already been associated with them. But then so has candy red. Which makes me wonder about the possibility of shifting.
Shifting blood colours in a single individual is kind of weird and impossible though. Then again. Different blood colours within a species is weird and impossible anyway so why the hell not? XD
Alternately, maybe they're part of the pre-scratch Alternian world. Although I kind of like the clone idea more. Given the things they seem to know and how they describe it as being from the ancient past.
Ahahaha. And thinking about this got me rereading that conversation between Dirk and uu again and that reminded me that I TOTALLY need to dig up that fic of them hateflirting and Dirk sending uu pictures of horse penises (because: irony!) again because it CLEARLY needs to be on my Kindle. And then when I go to look I find out that there is now three fics about them. Which is awesome. I have to see if the other two are worth saving. Because if there are any characters in this comic that I'm going to want to read fic about, it is these two.... and also possibly the Auto Responder.