GL_INGR_color_clamp
http://oss.sgi.com/projects/ogl-sample/registry/INGR/color_clamp.txt
	GL_RED_MIN_CLAMP_INGR 0x8560
	GL_GREEN_MIN_CLAMP_INGR 0x8561
	GL_BLUE_MIN_CLAMP_INGR 0x8562
	GL_ALPHA_MIN_CLAMP_INGR 0x8563
	GL_RED_MAX_CLAMP_INGR 0x8564
	GL_GREEN_MAX_CLAMP_INGR 0x8565
	GL_BLUE_MAX_CLAMP_INGR 0x8566
	GL_ALPHA_MAX_CLAMP_INGR 0x8567