Best shampoo for coloured hair?

I have the same problem so have a few darker lowlights put in which helps.
I use touch of silver shampoo and Tigi conditioner for blonde hair.
I find washing my hair less and using dry shampoo helps as does covering my hair in the sun.
Primark dry shampoo for blondes covers the roots in between visits to the hairdresser.

Tresseme do a couple of shampoos and conditioners for colour treated hair, I find the sun lightens my hair colour so the fresh colour doesn't last as long as in the summer months