According to John, it was about a drawing that his son drew of a woman named Lucy in the sky with diamonds.
I think that John was FOS. That song was inspired by, if not about, LSD. It just wasn't acceptable to write a song about drugs at that time, so they had to make up something to reduce the controversy.
Agreed. There's no way that song wasn't drug-inspired (or induced!) That said, it has some fascinating lyrics that are fun to visualize... they're very abstract, but not bad