I highlighted my hair and it turned a bright yellow.. like Lisa or Bart Simpson.. so I was told to use a medium ash color to get rid of the yellow.. now my hair is like a dark brownish gray! How can I get rid of the dark gray look? Any suggestions would be great.. thank you

I think you might have to go to a salon to have them fix it. Too much highlighting will damage your hair. It is hard to get an exact match if you are using at home mixes.

Your hair is gray because you used an ash color. That's like the number one thing not to do when trying to dye light hair darker. Using any type of darker cool color (ash) will make your hair gray/green. There are three types of "groups" I guess you could call them, when you are dealing with hair dye. Cool colors add more blue to your hair, natural colors keep the tones in your current hair color, and warm colors add more red. To fix your hair use a warm color, for example golden blond or golden brown. I hope this helps! :)