I dyed my hair blue about a week and a half ago. I had to bleach it because it was a really dark brown, but since it bleached unevenly the blue is greyish in some parts and really vibrant blue on other parts and on my roots it's a little blonde.
Sorry, but you'll need to bleach again. Blue doesn't get vibrant until your hair is pale yellow (almost white). Think of the colour almost like cellophane. Anywhere where it's still orange, and it will go a strange greyish or greenish colour.
On the other hand I don't think you put enough on - since it sounds like you did miss some of your roots, which being the newest hair bleaches the best and uptakes dye the best. It is easy to miss roots. You need HEAPS of dye the first time when dyeing with bright colours over virgin bleach, and you have to be very methodical.
I don't know how much money you've got, you could try putting a bit more blue on if you don't have much $, but if I was you, I would carefully rebleach the parts of your hair that aren't pale yellow (and now blue) yet. Use a brush, work in layers, get someone to help you or use mirrors/camera. Work as fast as you can - work in cold surrounds if you have to go slowly as this will slow down the bleaching reaction, then you can put a plastic bag over the whole thing and (very) gently heat it. Avoid your roots if they're pale blonde, else redo them. You may have to do a few passes. Conservative application of bleach is a little more expensive (as in don't put too much on for too long) but saves over-frying bits of your hair.
Also, whether your hair will take bleaching to pale yellow, especially on the ends, depends on how old the ends of the hair is, how you've looked after it, your health and age, and your type and thickness of hair. Some people's hair just cannot hack bleaching to pale yellow. My hair is thick so it can bleach pale pretty well provided it's not too long, but with age it's harder. You're probably young though.
Blue is the most difficult for a DIY beginner. Red (and purple to a lesser degree) will stick on unevenly bleached hair MUCH better. Use those colours in a pinch if you're in a bind, colour over the blue. Good luck.
I would not use bleach again so quickly. Why don't you try Kool-Aid in a vibrant blue and see how that works?
Sounds like you have received very good (professional) information and advice/suggestions.
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