Many people use dark nail polish to counteract the effects of taxane type chemo which can play havoc with nails - discolouring, lifting, thickening etc. I didn’t and I only got a very light, almost unnoticeable tan film on my fingernails, nothing else. My toenails, covered most of the time, thickened and went black, brown, grey and chalk white. I didn’t lose any but some lifted. So don’t think it’s sunlight! It’s the chemical reaction, and as with nearly all aspects of chemo reactions, it varies enormously. Good luck whatever you decide.