@dada I used black nail polish all through chemo and beyond. I didn't lose any nails, but they thickened and got ridges. 10 months after the end of chemo, my fingernails are only VERY slowly becoming less thick and uncomfortable, and are no longer flaky. A few of my toenails lifted, including the two big toes. They are still a problem, because wearing closed shoes (now that the weather is cooler) puts pressure on them and I've ended up with both big toes bruised black under the nail from the pressure.
It seems there's no clinical evidence to support wearing of dark nail polish, but I figured if anything MIGHT help ... besides which, the loveliest thing was that my daughter and a couple of friends here, plus two friends in France, wore black nail polish all through my chemo in solidarity with me!