There is a color which has a special meaning. This is called the inverted color and has the RGBA components (255, 255, 255, 0). Used mainly when designing cursors, the inverted color appears rarely on icons.
When projecting the icon/cursor onto any surface, colors of pixels under these areas become inverted. This makes cursors be visible over almost any screen images. Below is an example of a cursor which takes advantage of the inverted color: (This cursor is used by the Greenfish Icon Editor program itself and can also be found in the Samples folder.)
Notice that the circled area was drawn with the inverted color. Thus, the cross looks white over black and black over white areas.
Warning: The inverted color can be preserved only when saving in ICO/CUR format and only when using a color depth different from 32-bit. Otherwise, it will be replaced with the transparent color when saving the document.