The solution below assumes that:

(1) control 22 is a combo or a listbox.
(2) your colors are listed in the same order as they appear in the ctrl+k box.
(3) 'white' is the first item, then black, dark blue, green etc.
Code:

on *:DIALOG:away:sclick:33: { set %away.lcolors $calc($did(22).sel - 1) }