@Test
public void testSubtract() {

  final ColorRGBA clr1 = new ColorRGBA(ColorRGBA.BLACK_NO_ALPHA);
  final ColorRGBA clr2 = new ColorRGBA(ColorRGBA.WHITE);
  clr1.subtractLocal(1, 2, 3, 4);
  assertEquals(new ColorRGBA(-1, -2, -3, -4), clr1);
  clr1.subtractLocal(-1, -2, -3, -4);
  assertEquals(ColorRGBA.BLACK_NO_ALPHA, clr1);
  clr1.zero();
  clr1.subtractLocal(clr2);
  assertEquals(new ColorRGBA(-1, -1, -1, -1), clr1);
  clr1.zero();
  final ColorRGBA clr3 = clr1.subtract(clr2, new ColorRGBA());
  assertEquals(ColorRGBA.BLACK_NO_ALPHA, clr1);
  assertEquals(new ColorRGBA(-1, -1, -1, -1), clr3);
  final ColorRGBA clr4 = clr1.subtract(0, 0, 0, 1, null);
  assertEquals(ColorRGBA.BLACK_NO_ALPHA, clr1);
  assertEquals(new ColorRGBA(0, 0, 0, -1), clr4);
}