doimus: define "choose colours". The PC-Engine has an 8-bit processor but a 16 bit graphics chip (which handles 9 bit graphics, meaning a total of 512 colours to choose from), so I guess that is halfway.
Also, 8-bit would generally refer to the processor of a machine, and there it just means how big a single instruction can be or something, from what I understand. It really has nothing to do with the graphics as such.
And if you go into graphics 8-bit could mean different things:
It could be the size of the indexed palette, allowing for 256 colours at once (which is the case for VGA games.)
Or it could be the bitdepth, which then would mean either 233, 323, or 332 bits per pixel, or possibly even other combos like 2321 or 2222 with an intensity or alpha bit.