A palette is a collection of at most 256 colors used by 8-bit graphics. SLADE comes equipped with a large range of standard palettes taken from various games. You can choose which palette to use to display game graphics from the palette selector in the tool bar. When the "Existing/Global" palette is chosen as by default, SLADE will use the PLAYPAL lump from the base resource archive, if any. Slade also contains a grayscale palette as a fallback default option.
You can add additional palettes to SLADE's palette manager when viewing a palette lump. The entry view panel (in which the palette is displayed) need to be wide enough to allow the "Add to Palettes" button to appear to the left of the "Revert Changes" and "Save Changes" buttons.