Sonic Jam 6/Art Editing
From Sonic Retro
Levels
Level Palettes
At ROM:16CA, there's the instruction lea (off_EC66).l,a3, which specifies the address where there is the array of pointers to level palettes. Then (usually at 0xEC66) you find an array of pointers. There's a pointer for each level map, and this pointer points to the four palette lines for the level. Once you go to the address specified by level palette pointer, it's very easy to modify the palette. There are four palette lines in standard Megadrive format.