Hello Littleangels. 
I was told a few months ago by the hospital hairdresser (who fitted my cancer wig) that I could use Daniel Field's vegetable based hair dyes during chemo. It's available online. I didn't bother in the end as my grey skinhead hides my bare patches well! But she gave me a struck warning not to use anything else. Don't think she works for them, lol! 
Give it a go. Good luck x

Hello Littleangels
It isn't a good idea to use chemicals on hair either during chemo or within the first 6 months after stopping chemo. This is because the hair is very susceptible to damage and you could find that it breaks or falls out completely. The chemicals used in chemo also react with the chemicals in the dye and could cause a completely different reaction.

Many members feel the same when their hair started coming back between chemo sessions so please don't feel that your friend is alone in feeling this way. I know one of our members spoke to her oncologist about the options and they were advised either a vegetable dye or natural dyes. A couple to try are Daniel Field's Watercolour (which Larbel has also mentioned in their post) or Herbatint, which are formulated without ammonia.  A good alternative if your friend simply wants to disguise roots or colour re-growth is a tinted styling mousse.  These wash out every time you wash your hair, but are a safe, quick and easy alternative to harsher dyes and tints, until you are able to start using other products again.

I hope this helps. 

Best wishes, 
Jenn
Cancer Chat moderator