hi @Kazmar. Good questions! I'll start off by telling you what happened to me.
I had dyed ash blonde long curly hair and I suspected my natural colour was almost all over grey too. My hair came back in thick and curly and platinum but very coarse and wiry. I used the 'natural' hair dye Herbatint Ash Blonde from a health food shop about 5 months post chemo but it hardly did a thing. I waited another 6 weeks and went to my hairdresser who dyed it with my old colour and again, hardly a difference.
Waited another 8 weeks and my hair seemed to be getting softer as it grew and finally 6 weeks ago I went back to my hairdresser and the colour took. So all up nearly a year since I had it shaved did it feel and 'act' (!) like my hair again. It also tied in with finishing a year on Herceptin so maybe there's a link there as well.
It's still curly and I don't think I'll go back to having it long again but I feel more like my old self when its coloured.
Glad you're over the worst of it and good luck with everything! x
