There are often mistakes made with colour in The Simpsons. This is because the colour gets put on the cells in Korea where they sometimes mistranslate the instructions. Mat Groening said in an interview that they often have to send the cells back but if it's only a minor mistake they don't worry about it. In the "Bart's Comet" ep. where everyone is walking up the hill behind Ned joining in the song, Apu has yellow skin the same as everyone else (this is mentioned in the Simpsons guide). There is a couch gag with the family running in and sitting down in black and white and then Korean people run in and add the colour with paint brushes-there is a slight mistake with the eye outlines but I don't know if this is in reference to the real life mistakes.
How 'bout Hans Moleman (you know, the little old guy who keeps getting hurt for no reason) changing from black to white all the time? Even Michael Jackson only did it once!
in the episode where the simpsons (and the rest of springfield) gets robbed by the cat burglar, marge loses her pearls, then just pulls another strand from a big ball of 'em she keeps in a drawer. they were ALL red.
In the episode where Bart fell in love with the reverend's daughter, he said, and I quote, "Is it the fact that I've worn the same clothes day in and day out for the past four years?" That explains that Bart has worn the same exact clothes since he started first grade. I know that he said that because I have that episode on a video cassette. I also have the episode where Marge's pearl's are a different color than they are in the next scene. It is the episode where Marge starts to bowl with that French guy named Jacque (I think that is how it is spelled).
Westopher......apparently Smithers being brown is a stuff-up by Klasky-Csupo. They intended him to be yellow like the Simpsons all along. Someone from the Simpsons suggested we imagine he had just returned from a holiday with a tan.
In regards to the Smithers being brown in the early episodes...he is not brown he is black...but obviously they cant paint him "black" just like Lou the cop...hes black but just painted brown. Anyway, the creators did not want a "black" person to be Burns' assistant becuase this would have made it look pretty racist, ( a black man working for a rich white man)