free_colors(+Colormapable, +Pixels)
     free_colors(+Colormapable, +Pixels, +Planes)

Pixels, a list of pixel values allocated from the colormap associated with Colormapable, is freed, so that those pixel values can be allocated later. Colormapable defaults to the default colormap of the default screen. Planes, if supplied, is a list of plane masks, which is also freed.