In general, the appearance of an active or selected gadget changes to
inform the user the gadget state has changed.  A highlighting method is
specified by setting one of the highlighting flags in the Gadget
structure's Flags field.

Intuition supports three methods of activation or selection highlighting:

  * Highlighting by color complementing (GFLG_GADGHCOMP)

  * Highlighting by drawing a box (GFLG_GADGHBOX)

  * Highlighting by an alternate image or border (GFLG_GADGHIMAGE)

  * No highlighting (GFLG_GADGHNONE)

One of the highlighting types or GFLG_GADGHNONE must be specified for each
gadget.

 Highlighting by Color Complementing 
 Highlighting by Drawing a Box 
 Highlighting with an Alternate Image or Alternate Border