A subclass of Fl_Button that indicates the "on" state with a light-up indented area. These were a unique feature of Forms and widely used by SGI applications based on it. I changed the drawing code to make a thin-edged light like Flame uses.
down_color() is the color of the light when the button is on. By default this is yellow. Color() is the color when it is off.
Fl_Light_Button(int x,int y,int w,int h,const char *l =
0);