face-differs-from-default-p

face-differs-from-default-p is a compiled Lisp function in `faces.el'.

(face-differs-from-default-p FACE &optional FRAME)

Return non-nil if FACE displays differently from the default face.
If the optional argument FRAME is given, report on face FACE in that frame.
If FRAME is t, report on the defaults for face FACE (for new frames).
If FRAME is omitted or nil, use the selected frame.