GL_ARB_color_buffer_float
http://www.opengl.org/registry/specs/ARB/color_buffer_float.txt
	GL_RGBA_FLOAT_MODE_ARB 0x8820
	GL_CLAMP_VERTEX_COLOR_ARB 0x891A
	GL_CLAMP_FRAGMENT_COLOR_ARB 0x891B
	GL_CLAMP_READ_COLOR_ARB 0x891C
	GL_FIXED_ONLY_ARB 0x891D
	void glClampColorARB (GLenum target, GLenum clamp)
