Don't buy it, the dye is awful and they promote it as professional. The ones from the supermarket are a thousand times better. It's not efficient at all, it caused irritation and my roots turned orange. Even after the second wash, it became even darker. With Wella, which I've been using for years, I have perfect results

I bought the 9 in bleached yellow hair and it did nothing, it was like I didn't even apply it.. I used it as a dye and as a refle and nothinggg. Maybe it didn't work on my own hair, I have thick hair

If you want to use it on hair that has been highlighted and you want a silver platinum color, I consider it to be the best thing you can use as a toner to achieve a clean result without any yellowish shade after bleaching.
Personally, I mix it with a 9 and a little bit of 10 volume developer from the same line because I want a bit more shine in the color, and the lower the volume of the developer, the less it affects the natural color of the roots.
I highly recommend it!