The gameboy colour (sorry color) had a bitmap mode where it could display a stupid amount of colours onscreen at once,
maybe the snes had that too? but i don't recall seeing it in any games.
256 colours is ok or most pictures, Donkey kong country looks ok with that limit on it's prerendered sprites and backdrops.
In my opinion, any game that is 2d looks Snesish so long as it is quite colourfull,
8 bit games looked more distinctive given their limitations, and a Megadrive game would usually have a lot of dithering when compared with a Snes game.