A GIF palette defines colors using the RGB color model.
RGB stands for red, green, and blue—the three additive primary channels used to describe each palette color. In a GIF, pixels do not usually store full color values directly. Instead, they store indexes pointing to entries in a global or local color table, where each entry contains red, green, and blue values.
GIF’s indexed-color design was practical when many computers displayed only 256 colors at once. A color table can contain up to 256 entries, and each color channel is represented with 8 bits, allowing the palette entries to draw from millions of possible RGB combinations. The image itself, however, can use no more than the selected palette entries.
A common mix-up is confusing RGB with the file’s palette-index mechanism: RGB describes the colors, while pixel data refers to those colors by numeric indexes. YUV and HSV are other color models, but they are not the model specified for GIF palette entries. Dithering can simulate extra shades by placing different palette colors close together.