My natural colour was mousy brown but I've mostly had it coloured varying shades of blonde for most of my adult life. I've been colouring it myself for years now and was using shade 9.3 but even then white roots would begin to show after 4 weeks. So now I am using shade 10 and although I often think it's so light that it almost looks white, it is a perfect colour for me now as the roots hardly show.
My method is to mix up just half of the packet. Do the roots then immediately comb it through all my hair with a wide tooth comb. Leave for half an hour. I find that this way I don't get those awful lines where you can tell the roots have been done over and over. Then next time the roots need doing, I use the other half of the packet.
After a few root touch ups, I do use a whole packet to brighten up the rest of my hair.
I don't find it a bother, it's cheap and I can do it whenever I decide it needs doing. So for now I'm happy to carry on with it.
Ariadne xx