Back in the mid 50's I worked in a hairdresser and would have bright pink highlights in my dark brow hair. Always done myself at home. My father told me that if I lived to 50 I would be bald the way I was mistreating my hair.
When I did reach that age , I was dying (still done at home) my whole head of hair, thick and healthy, but the first grey hairs appearing. so disguised. I carried on doing this until I retired from work at the age of 70 and wondered how far down the full head of white/grey hair I had gone. Turned out at 75/25 - but decided then to stick with it and let that grey take over.
Thirteen years later I am delighted that I have the most wonderful head of silvery grey hair of which I am most proud. Still thick, needs thinning each time I have it cut.
The hair we can see can be damaged by harsh chemicals, but the root can still be very healthy.