I create a userlist with /auser and changed color in adressbook for this user(s) but the assigned color for it won't show.
Is there away to force this?

If the user doesn't highlight that's good proof that you either configured the address book wrong or did not add the right hostname-- otherwise mIRC would have properly highlighted the nick. Verify you set it up properly.

Found the problem. It seems (after reading help files and browsing internet again) that the order of appearance is crucial for getting it to work.
When it gets a match on first hit then the rest stops, so i put my highlight group on top and now it works.

Yes, just like in many (most?) things in mIRC, the first match will trigger and then it will stop looking. This is true for script events, user lists, address book entries, $read, etc.