Apollo 9 Command Module
Here is an excellent group of photos of Apollo 9's CM. You should be able to see the variations in the panel colors, which range from off white to light grey to medium grey. It appears that the main console and any other panels with switches or controls are a medium grey, while the remainder is a lighter grey. Naturally this may vary between spacecraft.
These photos are courtesy of Stewart Bailey of the Michigan Space and Science Center.
Read MoreThese photos are courtesy of Stewart Bailey of the Michigan Space and Science Center.