Splash Hill for Genesis

[Dolphman]

Well you have four palette slots in Genesis/MegaDrive games that can hold fifteen colours with the sixteenth being used for transparency.
So the Sonic games' palette slots pretty much went like this:

First slot - Playable character, Dr. Robotnik, some Badniks, objects and items
Second slot - Some Badniks, objects, and items like rings
Third slot - foreground tileset. Sometimes certain in-level objects
Fourth slot - Background features like the ones that use parallax scrolling.

Hope that helps, unless you know that already.