Growing up watching the Simpsons I always wondered were the citizens of Springfield white. I literally just got my answer watching Season 3 episode 1 "Stark Raving Dad." In this episode Homer is committed to a mental institution and while there he befriends a guy who thinks he's Michael Jackson. Homer doesn't know who Michael Jackson is and he believes him. Homer invites him to his house and through word of mouth the whole city shows up to see Michael Jackson. Everyone is highly disappointed when the guy steps out the car. You can hear everyone saying different things, "This guy is 300lbs", "He's white."
Finally a life long question answered.
Deep down I always knew the citizens of Springfield were white because Apu from the Kwik E Mart is Indian and Dr Hibbert(based on Bill Cosby) and Carl are clearly black. The ethnicity of the Simpsons characters are not a big deal to me just a gee whiz question I always thought about. I can't believe they are still make new episodes, this the greatest show ever.
SIDENOTE- I forgot to add "Bleeding Gums Murphy" clearly black.