A custom palette is optimized for the display of a particular image. An image displayed using a custom palette results in an image that is most like its original.
Using the custom palette has one disadvantage, which is only noticeable when displaying multiple images using a monitor and controller that display 256 or fewer colors. The disadvantage is that background images can appear in lower quality than their originals. This occurs because Windows shares the active palette of the foreground window, which may not be suitable for displaying background images.