Here goes.
Situation:
I'm late fifties. Hair used to be blonde (level 7 or 8) but has darkened & greyed over the years. It's now iron grey, about 50% white, but I colour it with "Natural Baby Blonde" which is a light neutral blonde. It looks ashy because of my whites - or natural highlights, as I choose to call them 
My skin tone is pink, but also a bit sallow. I have blue-grey eyes. When I used an "Ash Blonde" box colour it looked dreadful, but I also look grim with red hair. So I must be on the cool side of neutral, is that right?
Ambition:
Clean white hair with silver & grey lowlights. These are what's causing my problems!
I like this, this and this.
Possible solutions:
I can bleach the hell out of it and use white (violet) toner. But that'll make it too samey, and I'll keep running out of toner when it goes yellow.
I can bleach in highlights, then use grey (blue-violet) toner. It might not work and, again, there's the problem of relying on temporary colour.
Use one of the ultra-light box dyes, like John Frieda Extra-Light Beige or L'Oreal's 10.21 Pearl or 10.1 Ash. Then highlight over that with a froster. But will that just look like an '80s blonde, rather than assertively silver?? Argh!
I kind of hoped I'd be able to find out how to do it properly, using a Majirel mix, but can't find out what shades I'd need to use.
Doesn't anybody do permanent grey & white colours??!
Shades:
I know I'll have to use a 'silver' toner to keep it frosty (assuming I ever get to frosty) but don't really know how to identify the tones I need or should avoid. Is 'Pearl Blonde' too pink, for example? Should I be looking to blue-based or purple-based shades?
Am
and need advice!