The Mask File text field displays the path of an icon color mask. A color mask defines the region of the icon to which the background color is applied. You can think of this as a stencil cut out overlaid on top of your icon before the background color is applied to the icon. If no icon mask file is specified, the entire icon is colored with the background color.
The icon mask does not have to be a 32 by 32 (XView format) pixel icon. If it is larger, only the first 32 by 32 (XView format) pixels in the top left corner of the icon are used.
For example, Figure 16-6shows the icon and the icon mask for the printtool-prog Binder entry. The image on the left is the icon image, and determines what is outlined in the foreground color. The image on the right is the icon mask, and determines the area of the icon colored with the background color.