Grey formula

[Donnalm]

Hiya,
Can anyone tell me what is a good formula to use to create grey colour?
I use revlon professional colours.
They have grey colours 011, 012, 017 etc but find some can be rather blue or violet

 

[Fabby]

The best thing would be guy tang mydentity! 8 or 10 SS on prelightened white hair! Salon services carry them