This is why it's important to be a brow artist/designor and not just a waxer. The majority of people that will walk in our doors will not have much to work with. We need to know what to do, to make them look better than when they walked in.
I have two shades of pencil that I offer, Nut Brown and Blonde. Just the two shades are enough to accommodate 99% of the people. You can vary the intensity of the color by your application so it can be very light to dark. Yes I do show them how to use the pencil and make sure they go home with one.