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.
Then how committed are you to your color choice? In other words are you ready for a permanent change or are you still dabbling so that semi_permanent color would be a safer way to go?