How can I lighten my black dyed hair? I've only dyed it black/blue twice. I want to start putting caramel highlights in gradually and then start putting proper blonde hightlights in. When I asked my regular hairdresser she said it wasn't possible as nothing will lift the black colour in my hair and the only thing I could do is strip the colour gradually by using washing up liquid once or twice a week.

Lightening gradually is a crap shoot at best (damage accumulates). Also, lightening black hair requires that you use color remover to remove the black pigment before you can lighten (bleach). Your colorist is also uninformed about "gradually" stripping the color. ColorFix, Color Oops, or Color Zap can remove the color, but just for highlights, I don't think it's reasonable.