I first heard about Fanola No Yellow shampoo on you-tube, while watching a hair dresser using it to replace the in-salon toner and the results were phenomenal. This shampoo can be used as a post-lightening toner, or used to maintain the cool tones in your blonde highlights when things start to turn brassy.
It is a really powerful purple shampoo. It will stain your hands. I have seen Fanola No Yellow turn yellow hair into a nice neutral tone. I would have to say this is one of the most powerful purple toning shampoos I have ever used.
Although its great for blondes to use when needed, alternating with a decent moisturising blonde friendly shampoo and conditioner is a necessity as I find that over-use of this shampoo can dry out the hair and lead to breakage.
Also, if your hair is turning dull and brassy, consider using a cleansing shampoo first before something like this to remove and build up, then brighten with this shampoo (used sparingly though as your hair will be porous after cleansing, consider diluting it first).