OpenGL Programming Guide

Chapter 5Color

Specifying a Color and a Shading Model

Specifying a Color in Color-Index Mode

In color-index mode, use the glIndex*() command to select a single-valued color index as the current color index. void glIndex{sifd}(TYPE c);
void glIndex{sifd}v(const TYPE *c);

Sets the current color index. The first suffix for this command indicates the data type for parameters: short, integer, float, or double. The second, optional suffix is v, which indicates that the argument is an array of values of the given data type (the array contains only one value).

Advanced

The current index is stored as a floating-point value. Integer values are converted directly to floating-point values, with no special mapping. Index values outside the representable range of the color-index buffer aren't clamped. However, before an index is dithered (if enabled) and written to the framebuffer, it's converted to fixed-point format. Any bits in the integer portion of the resulting fixed-point value that don't correspond to bits in the framebuffer are masked out.

OpenGL Programming Guide