I hate to disappoint, but there is no texture that controls the background color. You could edit some files, and then some other files, and then edit more files, but it would be a lot of work. Then, the colors would still be off when you use some of the reversionary modes, because those are baked into the model file. The colors you see in the manual are either a product of the lighting, or color correct applied to make the screens more readable. Sorry to disappoint.