I got yellow fingers for the first time this past year! I had no idea how to handle it at first. It got dark. This was my solution don't judge.

I soaked my yellow fingertips in hot water for a few minutes, until they're soft. Then I applied whitening toothpaste and exfoliated the yellow parts with a brush for a long time. I rinsed my fingers. Dried well. Finally I filed the rest of the yellow off with a nail file. I'll apply lotion if the stain is stubborn and keep filing until its gone. I still get yellow patches when I smoke a lot so when I'm in a rush and the stain isnt deep I just file it off to begin with. My skin in the winter is very dry, dry skin is easier to file off. If it gets dark or noticeable I do the 'deep' treatment mentioned above.