Colouring your hair yourself is never going to be easy. You will be beset with challenges from the very beginning – how do you reach the back? Have you sectioned your hair properly? Have you got an even covering? In short, it is not a great idea to colour your hair yourself. You should get a trained professional to do it in a hair salon.
Book into a salon that is going to be able to do a good colouring job for you. Choose one with a good reputation that is a hair colouring specialist. Book in for a consultation initially, to decide what you would like to have done.
If you do still decide to colour your own hair, make sure that you always do a skin test first. You can become allergic to hair dye at any point, so even if you have coloured your hair before, carry out a patch test.