First off you HAVE to bleach it, or else your color will never come through.
Now we have to face facts. Your hair is naturally the darkest it can be,meaning you can never bleach your hair to a very fine yellow or almost white. Unless you risk losing your hair, or fucking it up, bleaching it more than once.
Now, in simple color theory, what colors do yellow and blue make?
You won't end up with a solid blue, even if you do, once you start to wash it, it will fad pretty damn quick to an ugly green.
So, if you can get it bleached to a pretty much yellow, choose something that fads to a decent color, or less blochy color. like purple or red.