Customize FACE, which should be a face name or nil.
If FACE is nil, customize all faces. If FACE is actually a
face-alias, customize the face it is aliased to.
If OTHER-WINDOW is non-nil, display in another window.
Interactively, when point is on text which has a face specified,
suggest to customize that face, if it's customizable.
(fn &optional FACE OTHER-WINDOW)