I think choice and feeling like you need to because of others is different.
I've dyed my hair since I went grey at 20 because society told me grey = old and past it. At 40, I grew my colour out because I got fed up with being made to feel bad for being grey (the real me). If I was grey, I wasn't good enough.
When I stopped dying my hair, I felt less pressure, had more money, more time, less stress, better condition hair, was teaching my daughter that all hair colour is beautiful etc. And yes, less environmental impact. I was dying my hair because I felt I had to survive within strict societal expectations.
I kept my grey hair for 2 years. Then I decided that I missed changing my hair colour. So I started dying it again but this time, I was actually choosing to dye it. Sod society, I wanted my hair this colour.
@IstanbulConstan has a point about not showing the real you and making others feel inadequate for not making "desirable" changes however, we don't know if HW changes her hair colour because she needs to (like me before) or if it genuingely makes her feel happier (like me now).
Visible women do impact on others- why else would a hair dye company pay her to dye her hair a certain colour? She is encouraging women to change themselves.