I have medium dark brown hair with lots, lots, lots of bleach blonde highlights.  Often the highlights turn brassy and yellow and I've used many blue or purple hued shampoos to try and counteract this problem.  This shampoo does the best job by far.  I can enter the shower with yellowish highlights and exit with perfectly bright cool toned white/ash highlights.  My hair lady tells me this happens due to hard water (which I have) but since I've found this shampoo it's not a big deal.  I probably use it two times a week.  It's not easy to find but I did buy it at Ulta.

Ingredients:  water, sodium laureth sulfate, PEG-7 glyceryl cocoate, sodium chloride, disodium cocoamphodiacetate, glycol disterate, sodium benzoate, benzophenone-4, laureth-4, laureth-2, polyquaternium-10, coco-glucoside, glyceryl oleate, fragrance, carbomer, glycine, salicylic acid, cocamidopropyl betaine, propylene glycol, PEG-55 propylene glycol oleate, disodium edta, glycerin, citric acid, butylphenyl methylpropional, moringa pterygosperma seed extract, HC blue No. 2