GL_EXT_blend_color http://www.opengl.org/registry/specs/gl/EXT/blend_color.txt GL_EXT_blend_color GL_CONSTANT_COLOR_EXT 0x8001 GL_ONE_MINUS_CONSTANT_COLOR_EXT 0x8002 GL_CONSTANT_ALPHA_EXT 0x8003 GL_ONE_MINUS_CONSTANT_ALPHA_EXT 0x8004 GL_BLEND_COLOR_EXT 0x8005 void glBlendColorEXT (GLclampf red, GLclampf green, GLclampf blue, GLclampf alpha)