mask {
  mode: alpha;
  source: color {
    bounds: 0 0 30 30;
    color: red;
  }
  mask: color {
    bounds: 15 15 30 30;
    color: white;
  }
}

mask {
  mode: inverted-alpha;
  source: color {
    bounds: 50 0 30 30;
    color: lime;
  }
  mask: color {
    bounds: 65 15 30 30;
    color: white;
  }
}

mask {
  mode: luminance;
  source: color {
    bounds: 0 50 30 30;
    color: yellow;
  }
  mask: color {
    bounds: 15 65 30 30;
    color: white;
  }
}

mask {
  mode: inverted-luminance;
  source: color {
    bounds: 50 50 30 30;
    color: blue;
  }
  mask: color {
    bounds: 65 65 30 30;
    color: white;
  }
}