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.
When you use the services of a real professional, go to the appointment with an open mind. You may have your heart set of pale blond, but if the colorist can prove to you that a deep strawberry is really your best shade, listen to her. She is trained to match color with skin tone. She knows what will work, and what won't.