If your fingernails are yellow from eating an orange, smoking or from using nail polish, you can get rid of the yellow tint by scrubbing them with a nail brush and whitening toothpaste.
Fitness weblog Shape recommends this technique for toenails yellowed by dark nail polishes, but it should work well for other things that can turn your fingernails yellow.
For Yellow Nails [Shape via Pinterest]
Yellowing of the toenails is a fungal infection mostly? i don't think this is very good advice?
A s you said, this only affects nail polishes, not infections.
Also, doesn't whitening toothpase actually grind away layers anyway?