You definitely have to have a good consultation with the colorist. My suggestion is always to bring a color you're looking for or a color that's inspiring you.
Color is a little bit different from a haircut. With a haircut, you can become a little more adventurous. Color is something that will stay with you, especially if you're planning to totally change your color. What you want to do is just have some guide to show the colorist of what your direction will be. From there, the colorist will tell you if it works for you, if it doesn't work for you and [ask you] what's your lifestyle, if you want something easier. Sometimes color can become an obsession—a good obsession—but sometimes it can really be a problem if you don't have the right time to do it.
If you have a Pronto Colore pen, it's great because you can postpone for a week, two weeks, max three weeks. But eventually you need to go back to the colorist because discoloration is going to happen; the ends are not going to be even. When the new color is going to be put on, it takes a little bit longer versus someone who goes to the colorist every 30 days or 45 days to keep up the maintenance.