But emoji's are not derived from the Simpsons. They're derived from the yellow smiley face ideogram that originated in the 1960s, it was designed by the artist Harvey Ball.
It's yellow, not because it's supposed to represent whiteness, but because the company colors of the State Mutual Life Assurance Company it was designed for were yellow and black, and because it feels sunny, bright and positive. It's an anthropomorphized representation of the Sun, and does not represent a human with a specific skin color.