Does anyone know how to set the foreground/background color back to in the properties palette ?

I changed a field's background color to gray then tried to change it back to white. The problem is that the the field's prompt background color also gets changed to white but I want it to be gray. There isn't a separate "prompt background color" option - you can only seem to change its foreground color. The only solution seems to be to return everything to the default "unspecified" but I can't find a way of doing it.