Virtual member functions

• virtual void use_colors(ColorList *) - this function is used to set up this object to use the specified ColorList to store and retrieve data. By default, it will save the pointer and then call do_use_colors.
• virtual void color_changed(ColorList *collist, int c) - after a color has been changed via the GUI or a text command, the ColorUser must be notified of the change so that it can update any internal state. This routine is called when color c in the specified ColorList is changed. By default, this just calls the virtual function do_color_changed.
• virtual void do_use_colors(void) - this is called after a new ColorList object is provided. It is a protected function, and by default does nothing. It should only be defined if the derived class needs to do something special when a new ColorList is given, such as create a new color category.
• virtual void do_color_changed(ColorList *collist, int c) - this is called after a color in the given category is changed. It is a protected function, and by default does nothing. It should only be defined if the derived class needs to do something special when a color is changed, such as rebuild a display list or recalculate some data.