static void varyCircleWithColor(CircleWithColor l, int w, int h) {
  int i = random(3);
  if (i == 0) l.center = varyPoint(l.center, w, h);
  else if (i == 1) l.r = max(1, varyInt(l.r));
  else l.color = varyColor(l.color);
}