I’m going to do a proper hair dye blog post one of these days but until then:
I use Punky Colour from Jerome Russell and always have. Punky Colour seems to work the best for my hair and the color stays true for quite a while. Back in the day I always used “Atlantic Blue” which starts out true blue and fades to a more cyan color after a week or two. Now that my hair is super long and I need more dye, I’ve actually been mixing “Atlantic Blue” and “Turquoise”, which is what is in my hair currently. :) ”Turquoise” on it’s own was too green for my tastes.