extension ARB_texture_swizzle
+# OpenGL ES can't set all swizzle values at once
+optional GL_TEXTURE_SWIZZLE_RGBA
+# Individual color enums are not available in any reasonable extension; they
+# were introduced to desktop OpenGL very early and to OpenGL ES in 3.0 together
+# with swizzling
+optional GL_GREEN
+optional GL_BLUE