I don't know if what you need can be done directly with AutoCAD... if possible maybe someone will explain it. But here's what I usually do when I have something like this:
I'll create the drawing with the colors, linetypes, and weights that I want and print the file out as a PDF. Then I open that PDF with Photoshop. Files there come in as single layer transparent files. If I want a colored background I'll simply add a fill layer with the color I want and put the drawing layer on top of it. At that point you can flatten the file and save it out in any format you need... usually either JPG or BMP.
You don't need the full (expensive) version of Photoshop either. Photoshop Elements will work also, as will many other programs that can work with layers. This technique would allow you to put a drawing over a simple black or any colored layer, a textured layer, photo, or just about anything you might think of.
Hope this helps.
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Dave Hein, P.E.