I have a purple/blue vertical line going down the middle of my left thumb, from the bottom to the top of the nail. should i be worried?

Nail melanoma: Discoloration of the nail can be benign melanonychia, or represent a melanoma skin cancer. Hutchinson's sign represents discoloration onto the soft tissue at the proximal nail fold. If the color "bleeds" onto the skin, this can represent a melanoma. If it is not there is does mean it is not a melanoma however. Always best to have it evaluated.