Unfortunately I think the news reader defines it's own text color there, rather than accessing the standard colors set in the gtkrc file. Unless I'm wrong about that, it won't be easy to fix the issue while still keeping a black background :/

It's a lame workaround, but the desktop news reader applet works fine to browse titles, which you can then click to open into the reader and get the details. Since the titles list in the reader program is the only area with black on black, and the desktop applet provides a readable copy of the same list, you can get similar functionality. Like I said, it's not exactly ideal, but it does work for those who really want to use the theme but depend on the feed reader.