Background Goes Purple in Realistic Shademode

I do a few things with 3D and like to set the Shademode to Realistic now and then. My background is set to black which allows all the colored lines my clients use so profusely. But when I set Shademode to Realistic, the background turns to a purple-ish color, not the standard jet black background which i prefer. I'm not aware of how this is happening or how to avoid it ???

I'd guess the issue is in the color definitions. Try Options | Display | Colors. Set the Context to 3D Perspective and see what the Uniform background color is. It may differ from the background you normally use.