The problem is the skin you are using resets the system colors, too, so that unskinned apps at least look similar, so using a Per Application exclusion for Word3K, which is one option, might not solve the problem. You can try that, however, by going to the Per Application section of the WindowBlinds Configuration dialog and adding winword.exe to the exclusion list (you allow partial skinning if you wish in the dialog that comes up).
If that doesn't work, it is relatively easy to change those colors in the skin. Get SkinStudio from Stardock (free download), open the skin in SkinStudio and go to the Classic Colors section. I suspect the color you are having trouble with is the application window (the 'paper' color of the open document). SkinStudio is a bit counterintuitive here - the color shown in the front window of what looks like the Display Properties preview image is not the color to change. Click on the window behind it & change the background color there to whatever you like. You can also change the color of the Window Text (in the front window preview) if that's part of the problem. Save the skin, then reload or reapply the skin & see how it looks.