Hello,
Discoloration of the palms can often be associated with tinea nigra palmaris. It is a superficial fungal infection which causes dark brown to black painless patches on the palms of the hands and the soles of the feet. You can apply dandruff shampoo, which contains selenium sulfide, over the skin. Topical antifungal imidazoles may also be used, such as Ketoconazole.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.