I would consider using these palettes:

4 colors:

Black Red Cyan YellowBlack Red Green Yellow16 colors: ZX Spectrum palette with values 0, 170, 255. In other words, RGB combinations using 0, 255 or 0, 170.

256 colors:

This one is a subset of 9-bit RGB palette of 8 values for each, with LSBs of components merged like this:

`8bit 9bit (rgb)`

00 000

01 011

10 100

11 110

with the only exception being brightest color, which is white. Available pure colors are black, red, cyan, yellow and white. There are 5 true grays.

Subset of 12-bit RGB palette where 2 LSBs of components are merged. 16 grays available.

65536 colors:

A palette with 4 bits of red, green, blue and alpha (16 grays).

Another one:

4 LSBs of components are merged from 24-bit RGB. 256 grays.