Is the client a level 6 or 7 naturally with 70% grey/white?
Ash tones often trip up the unwary and as you’ve not said what colour house you’re using, if it’s Wella, the /1 is a grey ash (subdues but doesn’t neutralise) whereas the /1 in Schwarzkopf is a green based ash and in L’Oreal, it’s a blue ash.
Do you know if the grey in your clients hair is coarse and stubborn or does it cover easily?
Some colour houses recommend using their double base colours for a high percentage of grey or if it’s particularly stubborn.
Although it sounds straightforward, getting a mushroom colour without khaki tones can be tricky because unless you’re using something formulated specifically for a high percentage of grey, you need to pre-pig/fill the white hair with some gold and possibly copper tones depending on how dark you’re going, otherwise, it will look drab.
What colour house do you normally use?