I’ve lived abroad for many years and went to a shop and bought my hair colour in a tube and my hydrogen peroxide separately. I had white hair which I loved.
Since I’ve been back in the UK I find box dyes make my hair yellow and even using purple shampoo doesn’t get the white colour I want.
I have patchy grey hair as I am old now 
Where can I buy tubes of white hair colour and hydrogen peroxide - Amazon?
Also can someone please remind me what % of hydrogen peroxide I should use (9%?)
Thanks