Hello and welcome to healthcaremagic I would keep a possibility of Addisonian hyperpigmentation. In Addisonian hyperpigmentation brown-black discoloration is noted at various body sites: Involvement of face, oral mucosa, knees, elbows, dorsal hands and feet with periungual accentuation is characteristic. Nail discoloration is also noted. Vit B12 deficiency has been reported as one of the causes of addisonian hyperpigmentation, in otherwise healthy individuals. Vegetarians are at a higher risk for developing this deficiency because animal products are the main sources of vitamin B12. The hyperpigmentation is reversible with replacement of vitamin B12 levels. I would advice that you see your local care practitioner and get a prescription for a Vit B12 supplement. You could also use a cream containing one or more of the following skin lightening agents e.g kojic acid, hydroquinone, glycolic acid etc to bleach the already existing pigment. regards