Graphics.Rendering.OpenGL.Raw.EXT.BlendColor
glGetEXTBlendColor
gl_EXT_blend_color
gl_BLEND_COLOR_EXT
gl_CONSTANT_ALPHA_EXT
gl_CONSTANT_COLOR_EXT
gl_ONE_MINUS_CONSTANT_ALPHA_EXT
gl_ONE_MINUS_CONSTANT_COLOR_EXT
glBlendColorEXT