Try a little bit of concealer on lips, then follow with underage and oystergirl over top for that shimmer. Really, it totally depends on the pigmentation of your lips and skin.
Myth (or concealer) with Underage on top does that for me...exactly the same thing. (NW15 here, medium pigmented lips) From what I see in the other posts, I guess it really depends on the person!
concealer then pretty please just in the middle of lips a touch of c-thru and then cover w/ oyster girl! (pretty much from reading all the posts - same thing!)