Well, it is definitely NOT Roger. That should be obvious enough. Initially I thought it might be simply another track of Rick over top of what sounds like a double-tracked lead vocal... but now that I listen to that "midnight blue" in the second chorus... it sounds very Daveish. It's hard to tell; a lot of old Rick and Dave harmonies sound very similar. Though, I think in this case I'd go with Dave. It's definitely a Dave-like harmony.