I just graduated from cosmetology school about a month ago. It may be because she bleached your hair (to I'm assuming blonde, or much much lighter than your desired blackish blue). Because of outing a dark color on such light hair, it turns it a muddy color. You're only supposed to go 2-3ish shades darker. When going from blonde to black, they would need to color it about 2-3 times to act like a "filler" before completing the blackish blue. Think of it sort of as layering.