Shaving doesn't remove the shadow because the color comes from the roots underneath the surface of the skin. I cannot imagine trying to wax your upper lip, unless you have already done electrolysis and the hairs are re-growth. Not only would it be extremely painful, you could really damage your skin. Depilatories could also be an unwise choice. The skin under you nose is very sensitive! Please read the label of any product before attempting that.
Before I had electrolysis, I used Dermablend foundation, and it worked fairly well on beard shadow.
With kindness,
Terri