I started going grey at 21, and now most of the front is white. I did spend 4 years "natural" and got compliments, however I decided to go for a change, and went for a shade impossible in nature... and got loads of compliments. I think there is a shade range in which you will look good, depending on skintone and eye colour, and beyond that, you will look older, ill, or both. If you have to stick a ton of makeup on to look well with your chosen haircolour - maybe think again? I will never be a blond, in a million years - just would look completely wrong on me. Mind you one of my oldest and dearest friends always maintained she was a blonde trapped in a brunette's body.
As an actress, Catherine Huntley will be well used to switching hair colour - either courtesy of a wig, or dyeing her own. I liked the Louise Brooks bob she had a few years back - probably closer to her natural colour than most of the more recent ventures have been. I think, however much a younger Catherine may have suited such a light shade of blonde, as we get older our skin loses pigment as much as our hair. It's no accident that someone savvy like Liz Earle has been wearing a warmer and darker shade of blonde - it helps warm her skin up more than being as blonde as she used to be. Both Catherine and Alison Young should take note and go for something warmer and more flattering to their current skintone, rather than the skintone they had in the 20s or 30s.