Newbie Help, please - Navigation Bar

[D.M.M.]

I'm trying to change the background color to just a plain black. Seems simple almost too simple, but nothing I've tried is working. I'm using the "prometheus" navigation bar and "matched" it to my site (the grid site). I want the orange to pop up with mouse over, but I just want the background a plain simple black to "blend in" to the top, so basically all you see are the words, not the buttons.

The pictures are as follows:
1) shows the prometheus nav bar that I'm trying to get all black background
2) shows what I want it to look like
3) shows why I want the prometheus - because I like and want to keep the orange pop up with mouse over.

Thanks for your help!