In all the Forgotten Realms resources, it states that the drow were once called dark elves and that they had "dark" skin. Does that mean that they had black skin like they do in present day or more of a brown colour like that of people from Africa? It says that their "physical forms transformed to match the taint in their souls" or something along those lines. So my real question is how are the Ilythiiri different from the drow,aside from psychologically?
First off, remember in the Forgotten Realms that elves are the same size if not taller than humans. One can assume that the dark elves, since they are now shorter than all other elven sub races, where at one time taller. From sources that I have read, they have always had black (i.e. black) skin and light colored hair, but their eye color may not have always been the red that it is now, especially since violet eyes are seen as a throwback to surface elves in drow society.
Remember also that the drow banishment is at least in part an origin myth, and as such may not be exactly what happened. It may be that living underground in tight caverns caused the drow to start growing shorter, and the exposure to Faezress might have caused the change in eye color, as might have the development of darkvision.