Just as a pro-tip, NEVER forget if you Henna your hair, and be VERY careful if you ever dye it again, even if you think you've cut it all out. I used Lush Henna on my hair last SEPTEMBER(11') and on the 9th of this month I dyed my hair -- completely forgetting, because the colour was completely gone, that I had Henna'd my hair more than 6 months ago.
THIS is what happened to my hair, LOL. Of course, we still dyed over it fine -- but the dye overtop of the henna didn't last very long(red, normal) so now my hair is purple.
Be careful!