Shampoo for brightening highlights

[Menssanaincorporesano]

Hi there, does anyone have any recommendations for a highlight-brightening shampoo?
Mine look great when first done- all bright - but seem to fade after 3-4 weeks. I don't think a silver treatment would be appropriate because there's no brassieres.
Thank you!

Brassiness!

When I had blonde hair I used aveda blue malva, it is a brassy tone reducing shampoo but when my friend came over and used some her hair was brightened with one use! (She's naturally blonde!)

It's good stuff, I now have dark hair and use black malva instead - swear by their shampoo, seems expensive for a big bottle but I only go through 1, maybe onto the 2nd bottle per year, so it works out much cheaper than buying small bottles of whatever else

Thank you, that's really helpful- I'll look for it!