protected static void flipTripleColor (CNode n) {
		assert n != null : "n != null";
		assert !n.isLeaf && !n.left.isLeaf && !n.right.isLeaf : "!n.isLeaf && !n.left.isLeaf && !n.right.isLeaf";
		
		n.color = !n.color;
		n.left.color = !n.left.color;
		n.right.color = !n.right.color;
	}