My hair black and I want it to go blonde with blue in will the blonde cover my black if I bleach it? *

It all depends, there many question to be asked here!
First when you say black, are you talking about your natural black hair or color black hair?

If natural, then there is a possibility of becoming blond yet you have to take into consideration that it won't be a platinium blond but a orange/yellow blond which can be said as strawberry blond! Only with time it might become lighter! However you need to bleach it and just so you know it will ruin your hair. I would start by doing streaks first and add more and more with time!

If it colored black! Then FORGET about it! YOu will loose your hair! They will be sooo damaged and they will fall off!

HOpe it answer's your question

If you want to go blonde and blue, you will need to lighten your hair with a bleach mixture and then apply the selected colors. This is known as a double process. In this process, a color lightener is used to remove dark pigments from the hair in order to achieve your desired color. Hair bleaching is a difficult process and should only be attempted by professional. You should consider going to the salon to have this coloring process done.

A most common problem when people want blue hair but do it at home, they bleach the hair till it's blonde. BIG MISTAKE. Once you've bleached it to a blonde, and then apply the blue, your hair will turn out green. Why? Because yellow + blue = GREEN.
So you have to bleach it till it's white (which is very damaging!)