Firstly the hair isn't grey it's white and the more natural coloured hair you have determines how light or dark or salt and pepper you are.
How many blonde friends do you have that look grey? Because their hair is so light to start with the combination of the natural coloured hair and white hair generally makes their hair look cooler (in colour) & lighter blonde - this is an easy one as because the white hair will only be around 3 levels lighter than the natural colour it still suits skin colour, eyebrows etc and I think doesn't age.
The more difficult area is when your looking at very dark hair as the contrast 50% white so (salt and pepper) with a great hair cut, well conditioned ( as generally the texture of the grey hair is more coarse - hence fine hair women love the additional volume it creates) we'll blow dryer hair looks amazing and not ageing.
75% or more - the grey area I call it is tough as I think it requires and change in makeup in order to compliment skin tone, eyes etc
100% white I have only seen a few times in my 27 yr career is beautiful and timeless and certainly not ageing I think there is a softness it brings framing the face - still a must with a great hair cut etc as above
There are so many amazing true temporary options of colour in a range of colours via the professional salon as well as the high street now that really and condition and shine and give you choice and versatility during that growing out stage as well as once grown out
Growing it out is a different ball game and needs tackling with great temporary or partial colour and textured hair cuts
Hair care regime also makes the difference between hair that looks smooth, shiny hair that's cut and styled beautifully no matter what colour doesn't age it looks youthful.