system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is Bart Simpson wearing a blue shirt in merchandise?

I know he use to wear a blue shirt back when the Simpsons were just shorts on the Tracy Ullman Show, but I never figured out why he'd still be wearing blue on dolls, toys, posters, etc. after changing to a red/orange shirt in show.
gpt
A lot of fake merchandise was doing the rounds in the 90s, and official merchandise featuring Bart was given a blue shirt. It was a way of telling the consumer that any orange shirt Bart merchandise was fake.