I have naturally dark blonde hair with reddish undertones; I lighten my hair from a Natural 8 to an Ashy 9.5 and the brassiness nearly always finds a way to ruin the shade. I've been using this shampoo and conditioner for the past six months, and the more I use it, the brighter and more natural my hair looks. Which is a godsend, because it saves the color by making it healthier, rather than harsh alternatives, like "stripping" the color, or using a "color corrector"...brassy color is stressful enough!
I have only two issues: I wish the solution was a little stronger, so I could be completely rid of my natural golden blonde's brassiness; that there aren't any color renew styling products for this purpose.