If you have an image set as wallpaper, you will never see this desktop colour, but its setting affects the desktop icon font colour.
Something I have just realised is that when Windows computes the best shade of grey for the desktop icon font, it's not the wallpaper image (jpg or whatever) that it looks at, it's the underlying desktop colour. Transfusion has green icon text because he is using Iconoid, which overrides the as-installed Windows 7 greyscale behaviour.