When dyed brown hair colour fades, it can reveal red and orange tones that make hair colour look less rich and vibrant. You need a blue shampoo and Conditioner to remove the red tones and wash after wash your hair colour will become richer and deeper once again:

If you feel your hair colour has faded and you want to add some colour to keep it vibrant, then this Brunette Enhancing duo do just that, they also blend away first greys to allow you extend the time between needing to dye your hair again: