Careful: that's for DarkUI, not DarkUId DarN

Dark UI is just a dark version of vanilla. Dark UI wz inventory is just the dark version of WZ inventory. As far as I know, DarN already uses WZ inventory, so I wasn't sure what the OP was asking. There was a thread posted a little while ago (at most a month) that explained how to get DarN to remember that you want the icons to display - you have to switch something in the xml. The mod that updates the xml for you (sorry can't remember the name right now) won't save that setting since it's not configurable via DarN's in-game menu.
Edit: found the http://www.gamesas.com/index.php?/topic/1137905-darnified-dark-ui-question/ I was referring to. I think this will solve the OP's problem if he's still using DarkUId DarN.
Also found http://www.tesnexus.com/downloads/file.php?id=34792 that remembers the other settings. Forgive me, K, I'm getting old