All hail Wella Koleston 9/8, my all-time favourite dye. I worked with it a lot when I was hairdressing, since you can do anything from cooling a blonde, to correcting colour after bleaching, and to achieve a full-on pastel purple, which fades into a wonderful grey.
Since I hadn't used 9/8 for a long time when I bleached my hair recently, I second-guessed my memory and did the lengths in 10/81, which left most of the post-bleach yellow (though the 9/8 applied to the roots was perfect). I corrected it with a round of 9/8 in wet hair with 6% and it was immediately fixed. At this point I'll only need to freshen the colour up with 1.9% in wet hair after a month or something
I dunno what it is about Koleston 9/8 in particular, but despite trying many different dyes, semi-permanent colour, pigmented shampoos, etc. I've yet to find anything else with the same range and stick. My salon may or may not have been the one that ordered more 9/8 than any of the other salons in the same area that were a part of the same chain. 50% of the usage of it was probably on me 😂