The mystery was explained by former director David Silverman. In a 1998 interview, he revealed that colorist Gyorgi Peluci had to leave the family with one color just because Bart, Lisa, and Maggie didn’t have a line to separate their hair from their foreheads. If the skin color were more realistic, it would look like the characters’ foreheads had been «sawed off». The show’s creator, Matt Groening, liked the idea and decided that all the characters would be yellow because it was something quite different from anything released before then. From the beginning, Groening always wanted to distance his work from other cartoons because he was afraid that it would be rejected by viewers as “child stuff”. The “artificial” color generated a feeling of discomfort that helped the audience to face the show with different eyes.
– Why do animated characters have four fingers?