GL_EXT_cmyka
https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_cmyka.txt
GL_CMYK_EXT 0x800C
GL_CMYKA_EXT 0x800D
GL_PACK_CMYK_HINT_EXT 0x800E
GL_UNPACK_CMYK_HINT_EXT 0x800F