color selected text

[feng@.cs.umass.edu]

I am implementing an interface. The interface is designed as a dialog
window, in which there are several items, one of them is an editable-
text-dialog-item. I want to color or change the font of the selected 
text in the editable-text-dialog-item. The build-in method set-part-
color does not work for the selection range, but for the whole item.
Has anyone known some method that can make this change ? 

For example, the following code makes a dialog window in which an
editable-text-dialog item and a button-dialog-item are enclosed.
The dialog-item-action of the button-dialog-item should color or 
change the font of the selected text in the editable-text-dialog-item 
text-item, once clicking on the button.

(setq interface
	(make-instance 'dialog
	               :view-position 'centered
		       :view-size #@(250 250)
		       :view-subviews
			(list
	(setq text-item
	(make-dialog-item 'editable-text-dialog-item
	                  #@(5 20)
			  #@(100 180)
			  ""
			  'nil
			  :allow-return t))
	(setq coloring
	(make-dialog-item 'button--dialog-item
	                  #@(5 200)
			  #@(100 180)
			  "coloring selection"
			  #'(lambda (item) item))) ;;;I need the
                                                 ;;;coloring method here
	)))


Any suggestion is very welcomed, even without using the editable item.
However, both the table-dialog-item and sequence-dialog-item can not
be used for this purpose since them can not partially select a cell.
Thank you very much.

Fangfang Feng (fff in short)