I think you're safe. i had a G3 and bought a used battery for it. When the battery came in it was a diffferent shade of white from the original but worked no problem. That same battery now works flawlessly in, and matches colour-wise, my iBook G4 so I think it's safe to assume that they are pretty much the same.
“Maybe some day somebody will call me "Sir" without adding "You're making a scene"!!”