Well if you plan to use a 32 colour screen, then your animation also needs to be 32 colours and use an identical palette to the screen, even if you plan to separate the palette uses between the bobs and background.
Animation could of course be in 16 colours if it uses four bitplanes only. So animation could use the first 16 colours and background graphics last 16 colours.
This should open room for optimisations since 5th bitplane would always have all bits zeroed or all bits set.
