GIMP has two kinds of palettes. One is the color-map, also called an indexed palette, which is included with all GIF files, containing a maximum of 256 different colors. Indexed palettes can be automatically defined when you change the image mode from RGB to indexed, but you can also use a “custom palette” that has already been defined.
You can use any palette as a custom palette when converting an image to indexed mode. Working with palettes is like making a tapestry using a finite set of colors and interspersing those few colors to get the effect of a larger array.
Figure 22-60. The Palettes dialog and Palettes menu