Hair color isn't always about just "color". It's about shades, hues, and a good cut that will show off your new color. Perfect color doesn't come in a bottle. If you are hoping to get a color correction for past mistakes (caused either by you or another salon), it will take a real expert to add in the right toners to counter the faulty shades you are trying to get rid of.
Thinning hair? Did you know you can make it appear thicker by the strategic use of color? By that I mean if you color your root line to deal with any regrowth you're also making the roots look a bit darker. Not only does this touch up your color it will also create the illusion of thicker hair. That's because roots that are a bit darker make your hair appear to be fuller and more dimensional.