A palette, also known as a color lookup table (CLUT), is a correspondence table in computer graphics that assigns an index to selected colors from a color space’s color reproduction spectrum so that they may be referenced. This approach seeks to decrease data use, whether it is processing payload, transfer bandwidth, RAM usage, or permanent storage, by referring to the colors via an index, which requires less information than the one required to represent the actual colors in such color space. Indexed color pictures are those in which the colors are specified by CLUT references.

As of 2019, the RGB color model with an 8-bit per-pixel color depth is the most widely used picture colorspace in computing. Eight bits per pixel are required to express the brightness level in each of the RGB channels with this approach, requiring 24 bits of storage to completely describe the color of each pixel. Palettes are used to reduce the number of potential colors that must be handled at once (typically using adaptive techniques), assuming that each conceivable color is assigned an index, which allows each color to be referred using less information than is required to properly describe the color. A notable example is a 256-color palette used in the GIF file format, in which 256 colors are chosen from the whole 24-bit color space, and each is assigned an 8-bit index to represent a picture. While the system may possibly reproduce every color in the RGB color space (as long as the 256 color constraint doesn’t prevent it), the storage need per pixel is reduced from 24 to 8 bits per pixel.

The adaptive palettes of all shown image thumbnails may not be possible to be loaded into the hardware color registers at the same time in an application that displays several different picture thumbnails in a mosaic on screen. An approach is to utilize a single, common master palette, often known as a universal palette, which may be used to show an image with good fidelity.

This is accomplished by choosing colors in such a way that the master palette contains a “miniature” RGB color space, restricting the red, green, and blue components’ potential values. A consistent palette is a term used to describe this type of layout. The human eye is sensitive to the three basic hues in varying degrees: the more sensitive to green, the less sensitive to blue. As a result, RGB layouts can take advantage of this by giving the green component more levels and the blue component less.

A master palette constructed in this manner may hold up to 8R8G4B = 256 colors, but it leaves no room in the palette for reserved colors or color indices that the software could utilize for specific purposes. Using simply 6R6G6B = 216 (as in the Web colours example), 6R8G5B = 240, or 6R7G6B = 252, which gives room for certain reserved colours, is more generic.

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