I suggest using some orange black tones for kubuntu for a professional look and feel and more ubuntu-ish, so kubuntu wouldn't look like a generic kde distro.

Here is my desktop as an example:
http://img504.imageshack.us/my.php?image=kubuntuorangexj2.png

UPDATE http://img243.imageshack.us/my.php?image=kubuntuorange2zq6.png

UPDATE 2: http://img392.imageshack.us/my.php?image=kubuntuorange3lh7.png

UPDATE 3: (works better with this usplash theme) http://farm4.static.flickr.com/3171/2308465614_22c4dccfc7_o.png