I have used it. I had platinum hair and wanted to make it dark to grow out. It took two boxes to make it dark brown an then I'd dye it one shade lighter as time went on each passing month. I liked it while I was using it but hairdressers hate boxed color so if you plan to get color done at a salon just skip the boxes and go to them in the first place. It makes it harder or impossible for them to do what you want if there are other chemicals on your hair. It's kind of instant gratification (and I think fun) to dye your own hair so think hard about what you want to do in the future before using a box color.
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