Review (5/5): AMAZING COLOUR!!!! Truly an "electric" blue! Also really easy and reasonably mess-free.
Wow. Super-easy to use...I just combed it into a tween's blonde hair (no bleaching). Gave the colour great dimension with the various shades of natural blonde. Would be hard to use on dark hair without bleaching.
I left it on for about an hour, unwrapped. I cannot figure out how you'd blow-dry hair that's IN a shower cap as you do it (part of the instructions), so I just removed the cap and did the blowdry while gently combing through the hair with a comb (until dry). Then a rinse - this is where all the blue looks like it's coming out. Use cooler water.
We re-dyed every 7 days, and the colour stayed vibrant.
Since then, it's been about two months and the electric blue went to pale cotton-candy blue, then to teal, now it's the colour that blonde hair goes with too much pool chlorine in the summer (sort of a washed-out green). I've heard that you can get more colour out by using a "clarifying" shampoo, but the tween seems happy with the transformation.
No real mess, but the bath does have a faint blue tinge to the bottom from the rinsing. It seems to scrub out a little more with each regular cleaning.
WARNING: If you leave strands of blue hair on the counter and they get wet, they will leave thin blue lines on the Corian. This is true even days after you dye the hair.