customize-face is an interactive autoloaded compiled Lisp function in `cus-edit.el'.

It is bound to <menu-bar> <options> <customize> <customize-face>.

(customize-face &optional FACE OTHER-WINDOW)

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.