I have ash brown hair that I have to dye to keep it ash because with weather and washing, it quickly gets brassy. So no highlights but I have a few greys and 2 natural white streaks/forelocks. I can dye my hair and a week later, it's brassy. I have used a cheap purple shampoo from Walmart (Jhirmack Silver Brightening Ageless Shampoo) which is under $5 and it's worked fine, but I do get build up from it, so I can't use it all the time.
Thought I'd try this - at $17 a pop just for the shampoo, which is the only Joico item I bought (didn't need the conditioner) - this does not work for the price. My $5 Walmart purple shampoo does just as well, possibly better at darkening my brown (and it's cheaper!) I applied this on dry hair, then did wet for a few days - my hair has lost a little brassiness, but nothing to make this worth the price. I will continue to use it until it's gone, but I will not repurchase. The only plus I can see compared to my Walmart one is that this stuff leaves your hair clean and fresh - doesn't weight it down/have build up, nor does it dry it out. But for taming brassiness? Barely.