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.
Hair color product web sites offer the entire range of hair color available with them and what can be done with it. However, do remember that they are using professional models (with amazing skin) and you would need to discount some of the ideas that they demonstrate. The official web site however, does help you get the right shade and that is very important before you decide your hair color.