Jenn,  I would forget about the highlights and low lights for now.  Stick with one straight color, as you have already had too many chemicals put on your hair.  Go buy a box of Revlon Color Silk in light brown.  Use one ounce developer, one ounce color, and one ounce shampoo.  Mix it all up and color your hair as usual.  You use the shampoo with it to sort of water down everything, because as I said, you already have had too many chemicals on your hair in a short period of time.  Leave this mixture on for about 15 minutes, no longer.  This should give you a color you can live with for a month to 6 weeks, and give your hair a break from chemicals.  I believe your hair looks ashy from too much too soon.  Give your hair a rest, or it may all turn pure black and no matter what you put on it, it won't hold a color until all your hair grows out.  Your hair is your crowning glory, so take good care of it. 

Anna Sparky's Mom