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.
Hard as it is to believe there was once a time when those who colored their hair were looked down on by "respectable" women. Some would sneer, "She gets her color out of bottle, you know." Making it sound like that was a bad thing.