Black hair- Blue

Maybe put an actual dark-blue dye on, like from the Hot Topic or something? Just don't put it on bleached-blonde hair or it'll show up really blue. I've seen pics of what it looks like put over brown hair (I would've guessed medium-brown, but having just eyebrows to go by, I'm not entirely sure.) and it looked pretty close to black except where the light hit. I dunno, maybe it would work. I haven't tried it myself, though, for lack of dye money.

I agree with Kuroneko, get Specuial Effects in Electric Blue- it will be blue in your hair. You soak your hair in it, its a semi so it lasts through several washings, but it should give you the blue your looking for. You don't have to bleach first, just put some on a strand to test first- it should come out nicely.





I don't know whether Feria is* disapproved* of but it can't be removed with a color remover, it has to be bleached out. Depending how dark the color is and how many times the person has pulled the color through when doing roots( that seems to be a big problem in chemical processing), bleaching that color can be very damaging.
The bleach has to "eat" through all that processed color.
If ppl found a color they liked and stuck with it( on virgin hair) Feria wouldn't be a problem.

http://www.haircrazy.co.uk/ has a list of the different products, with reviews for some. I've used punky color in plum over dark hair and it looks fantastic, so far it has had pretty good staying power. They have a couple of blue shades and more, there is a decent color chart for it here: http://www.beautycentury.com/mall/resultcolor.asp?sku=3037

If you look at the Plum color, used over dark hair it came out much deeper and 'purple-er' and prettier than the swatch shows, so I would think the blues would be deeper also over dark hair.

Just be forewarned that this stuff stains *everything*. If you have a stainless steel kitchen sink it would be better to rinse your hair there; it's a real pain to get this stuff out of a white bathtub! It isn't so bad when you start washing your hair normally, just when rinsing the color out.