8-bit color is a color depth that can allow for up to 256 grays, or 256 colors assigned by a color lookup table (CLUT). This is referred to as "256 colors" on Macintosh systems, and the VGA standard by PC users.
Apple Computer implemented a "System palette" which included 6 levels of red, green, and blue in increments of 51 (on a scale of 0 to 255), that defined 216 uniform RGB colors. The remaining 40 colors were assigned to red, green, blue, and gray values that defined 4 gradients of 10 color values, and when combined with existing values from the 216, formed 4 smooth gradients of 15 values in increments of 17 (on a scale of 0 to 255).
Microsoft later implemented its own 256-color palette which assigned the first and last 8 values from its original 16-color palette, with the first 8 being lower-luminosity values of the last 8.
- Color Palettes (PDF) by Marc Johnson, Columbia University School of the Arts. 2020.