You can do this by styling the alternating text. You'll need to figure out the style of the alternating text, and then change it in your skin.
I'd recommend that you take a good look at the
DotNetNuke Skinning Toolkit and
also
Troubleshooting DotNetNuke Skins. The DNN Creative includes a lot of other tutorials about skinning that you may find useful as well.
I might also recommend that you set the administrative skin back to one of the standard skins.