The OpenGL 1.1 vertex array functionality lets you work with arrays of vertexes, colors, color indexes, etc. and call them individually, as groups, or as part of an interleaved array. (see "OpenGL 1.1 Vertex Arrays"). The index array format extension, SGI_index_array_formats provides additional interleaved array formats which specify index colors instead of component colors.
When the extension is present, the following tokens are accepted as the format parameter of glnterleavedArrays():
GL_IUI_V2F
GL_IUI_V3F
GL_IUI_N3F_V2F
GL_IUI_N3F_V3F
GL_T2F_IUI_V2F
GL_T2F_IUI_V3F
GL_T2F_IUI_N3F_V2F
GL_T2F_IUI_N3F_V3F