Dyed hair always goes brassy...

Using silver shampoo once a week definitely helps. Leave it on for a couple of minutes.

Ask you hairdresser to recommend a coloured shampoo. When I was still dyeing my hair a medium brown, it tended to go brassy as well, especially in the summer. I had a brown tinted shampoo by John Frieda that really helped.

Depending on your hair colour, their are tinted shampoos to counteract the fading.

Yes, the Elvive purple shampoo is good. My friend uses it all the time, as her coloured hair tends towards being yellow. I think it's common to have brassy tones if you colour it lighter than it's natural shade.

My original colour was fairly dark brown and particularly at the front it is mostly grey. For many years I have used Belle Colour no 6 light brown - I try to only dye the roots.
I’ve found it fades into a natural looking blondie colour which I am really pleased with.

Are you having any trouble finding the Belle Colour shade you like Thoro?
My shade is practically obsolete now.

BTW, purple or blue correcting shampoo or/and conditioner is helpful for brassy tones.
Elvive is heavy on the cheap perfume though!?

"Wella color fresh" is worth a look too. Recommended by my hairdresser.
I have pink tones (not bight pink just highlights) I add this conditioner just a few times between visits. I use lilac, it comes in lots of colours. 6 weeks later you can still see the pink.

My hair has nice n easy blond colour on it, my hairdresser recommended this last week as a toner, I’ve bought some, not tried yet.
www.amazon.co.uk/Fanola-No-Yellow-Shampoo-350ml/dp/B00RWCDM4A?tag=gransnetforum-21

Thanks everyone for the suggestions will look into them!