Advice Needed Desperately

Yikes!!  I would go back to the salon and insist they fix it, but I would ask for someone else.  Your roots are lighter because porous hair (color treated/dry) grabs the color more easily than non-porous hair.  You have a compound problem that will take several steps to fix.  You can do it yourself, but if it were me, I'd revisit the salon.

Hi!

I have posted other topics previously but now I have a new problem.  I spent many years dying my natural medium/dark blonde hair to a near white using a high lift color with 40 developer.  Last October I went to a salon and went back to my natural color which kept fading back to blonde very quickly.  Eventually I went slightly darker so that it would take longer to fade, but it still did.  Stupidly I decided to go really dark and my hairdresses put in a dark brown that looked black about a month ago.  I tried to wash with Prell to fade it but it wouldn't budge.  This past weekend I went to her to lighten it and it doesn't look much different except in the light where it looks dark brown.  My roots are also lighter than the rest of my hair.  I really do not want to go back to her again, but I need this hair to be a medium brown.  Is there any way I can do it myself or anything I can do to lighten it? 

Thank you!