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I would suggest you try to find a blue hair dye that you won't need to lighten your hair for.
Basicaly if you get a good dye that you won't have to lighten your hair it will be Dark blue when you put it in and as it fades (becuase most no lighten hair colors lost only about 6 weeks) the blue will start looking darker.

I used a dye that i don't have to lighten my hair for and it works well . my hair is naturally really dark and the red i used shows up so bright. It's only my bangs and a few highlights but it is crazy how well it shows up.
And as it has faded it starts looking like a darker red. Unlike my friend who is blond and as her's fades it looks almost pink.

i don't know the names ofany good brands though, not even the one i used xp sorry

These types of dyes usually do fade. The box will say about six weeks but it really depends on how often you wash your hair and how hard you scrub at it.
Me and my friend have had ours most recent dye job in for 5 and a half weeks and hers is still there but since her hair is lighter it is sort of lightish.
She also washed her hair a bit more often then i do. She washes her every other day or more depending on the days situations. . .
But because of my hair type i don't wash it as often . . .once or twice a week,
As far as these colors go, if you can kee your skalp pretty clean and if your hair doesn't get greasy too fast then using a shower cap instead of washing every day or every other day could be best.

your shamppoo will end up with a light tint of blue everytime you was your hair XD
If it is just a light tint then no worries, no tint at all than super, but if there is a lot of blue in the shampoo foam you might want to consider not scrubbing your hair quite as much or as hard.

as far as the initial dying goes just follow the instructions and you should be all set ^^

Do you have any hair supply stores near you??
Or beauty supply store. . .
something like that. . .

Well. . . at the sally beauty near me they have this stuff. . . i can't remember what it's called but it comes in blue, pink, red, and purple. . .
They don't have it on the Sally beauty website so i don't think i can be of much help. . .

What i would do is go in and go right to the hair coloring section and look for it. Make sure you read the boxes. . and yeah they would be in boxes.
If that doesn't work so well ask for help at the front desk or something.

If they have it but are out of stock or something just ask when their next shipment is and if it's on the order list.

I had to do that when i wanted to dye my hair blue because they always had the pink and purple but never the blue. . . i gave up on blue though cuz they never had it at the one near me. . .

i don't think they sell anyof it online.
Pretty much they show it on the website but it's usually only sold in stores.
I think thats pretty stupid though.
i don't blame them for not selling professional stuff over the internet but not letting people buy the stuff with the step by step instructions is stupid.

Hmm, I'll try to help if it isn't too late. xP
Well, I dye my hair ALL the time.

I'd suggest just using bleach first then dye the blue.

I use 3 different kinds of SEMI perminent dye.
Theres:
Manic Panic- shoppers drug mart.
Special Effects- Trivium.
Something that I get from Mama Cee's. ( A store to buy "african american" produces for cheap.)

The more you wash, the more the colour comes out.

The thing with Manic Panic's blue is that it starts of alittle dark, but after each shower it gets like REALLY bright, if you want pictures of my hair, I have. :]