Okay, so I ended up getting the purple shampoo from Clairol called shimmer lights from Revolution, but I was told that I'm only supposed to use it once a week to rid the yellow, brassy colour in my highlights or else it'd turn to a purple tint if I used it regularly. So what kind of shampoo should I use on a regular basis? One for colour-treated hair or specifically for platinum? Any suggestions/recommendations on products?