@missbattenburg
If the OP - along with millions of other people - is going grey in her 40s then 40s is not too young to be grey. We're all just fooling ourselves to think that it is.
You say this, and many many posters on mumsnet come onto threads like this EVERY single time, and claim that they have let their natural grey grow through, and sported grey hair since they were 32 or so.
Yet, in real life, I never, ever, EVER see women under 45 with their natural grey hair showing. I mean, never.
Another example of the parallel universe of mumsnet. 
I think the only people who are 'fooling themselves' are the ones who think having grey hair (especially in your 30s, 40s, and 50s,) is not ageing ... It adds ten years to some women. And yeah, grey hair does look better on men. Sorry, but it just does...........
The radfems can me what they like. Doesn't change the fact that natural grey hair showing through is very ageing, and looks worse on women than it does on men..
And by the way, it is not ridiculously time-consuming to dye your hair; it takes half an hour to 40 minutes, and needs doing once a month.
Funny how some people say dyeing your hair is so time-consuming, but think nothing of spending 5-6 hours a day (often more!) on message forums and social media! LOL.
Finally, @opinionatedfreak that woman you have posted a pic of (at 14.09 today) with dark hair, and grey hair, DEFINITELY looks better with it dark. The grey looks bloody awful. If you were trying to prove some kind of 'embrace the grey' point with that; you failed spectacularly!