VDP Palette
The MegaDrive have 4 palettes of each 16 colors. This means it can display 64 colors without any tricks.
Each of the color is composed of 9 bits (3 bits for R, G and B) so we have 512 possibility.
When writing to CRAM (See VDP data port) data must be this format :
Bit | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
Def | 0 | B | 0 | G | 0 | R | 0 |