Back when there were only three Star Wars films, given that, on the big screen, the light level in the scene cast the court members' skin as gray as the Emperor's, people assumed that the Emperor and his court were of the same nonhuman race, cf. Coruscanti.
Remember, this was the bad old days before CGI, when aliens had to be presented with make up, differences in skin color, and low-tech tricks like that.
The ultimate origin of Palpatine isn't exactly cleared up in the PT, anyway. Was he human and got scarred, or is his "scarred" skin his true appearance, unveiled? Screen canon doesn't say.
Making the Emperor's court all human frankly smells like a retcon, but I'll accept it. Han still shot first, though.