It's actually one of the easiest things in Skinning. It's like anything else. It's only about adding another style-attribute.
In the 1001 and 1004 definition change this line:
code:
<BuddyList id=atom(abView) Layout=FillLayout() CmdGroup=guid("{16E32D35-5350-4805-B7F0-5E782510AF6F}")/>
To:
code:
<BuddyList id=atom(abView) Layout=FillLayout() CmdGroup=guid("{16E32D35-5350-4805-B7F0-5E782510AF6F}") background=argb(0, 0, 0, 0)/>