http://lionking.wikia.com/wiki/I_Just_C ... King_(film)#cite_note-0
According to this wiki page, the DVD commentary reveals something a little disturbing.
Go to the trivia section, and you'll see an apparent explanation for the bright colors and trippy shapes in the song---apparently it's to "reflect the world through Simba's eyes".
Now, I know the cast and the story are fictional, but who would have thought Simba sees things so differently? I mean, does anything in this sequence look remotely like the movie during the non-musical scenes?
I dunno. Maybe I'm overthinking it. It's just startling, though.