"But if you use real Paralax-Scrolling on the Amiga, you have two layers with eight colours each or something like that"
I think the MAIGA could handle more than that.
One of the coolest things about the amiga games was it's many paralax layers.
The mega drive can only do 2 backgound layers. The SNES was the king in this field (4 layers)
I'll have to find the ISO of Filink It's SEGA CD.