Simpsons episode: What's the episode where bart and lisa ans students have to wear dull grey uniforms that tur?

that turn bright and tide eye when it starts to rain. That episode reminds me of a film we saw in elementary school when i was a kid, and i know The Simpsons always have a reference in their shows. It just brought back a blurry memory of a school film in which all these kids were wearing dreary clothes....can't really expalin it properly, but if i knew the episode it would give me a start on my research.