Once a basic color is determined, now comes the fun and creative part. She may suggest adding lighter highlights around your face and maybe even dispersed throughout your hair. Lighter color near your face can change your entire appearance without the permanent commitment of an all over change.
A good color means natural. Look carefully at a fistful of hair in the mirror. See how each strand has a different tone? Perhaps even different colors on one strand? These are the natural striations that Mother Nature gives each head of hair to work with natural lighting. A good "color job" must duplicate these natural highlights to be effective.