I've been using the violet toning treatment for about 3 weeks now and, unfortunately, without much result. I don't actually know what I was hoping it would do - probably neutralise brassy tones, but of course, it's not a 'blondening' shampoo so I was a little delusional.
My conclusion is that it doesn't really work on natural dark-ish blonde hair if you want it to go lighter and for it to bring out your natural highlights (if you have any). I will probably have people saying "that's not its purpose anyway!" which is fair enough, but it was worth a shot.
I did ntice after some washes that my blonde wasn't as golden - it turned a... greyer colour, a more dirty blonde, which I was really against. However, seeing as the change was completely insignificant, I didn't really mind.
All in all, this is probably formulated to work on coloured hair more than anything, molecules binding to receptors etc... so I wouldn't recommend it on natural hair, unless its grey.
I guess you can see the grey-ish tones on the left. Even though I said 7 washes, it's probably more than that. I felt my hair did lose some shine.
All in all, though the product wasn't exactly a waste of money at £2.03, it really didn't do much for my natural hair, so save yourself the trouble.
Hope this helps those wondering about natural hair!