WebGLState: Added clarification comment.

src/renderers/webgl/WebGLState.js

@@ -58,7 +58,7 @@ function WebGLState( gl, extensions, paramThreeToGL ) {
 				locked = false;
 
 				currentColorMask = null;
-				currentColorClear.set( - 1, 0, 0, 0 );
+				currentColorClear.set( - 1, 0, 0, 0 ); // set to invalid state
 
 			}