First off, don’t wear a wig unless asked to. While it may have worked for Vivienne in Pretty Woman, it’s probably going to shock the crap out of a client if it comes off in an inopportune moment. Use your own hair, and use it to its best capability.
In general, blondes receive more attention from prospective clients. This could be because of the old blondes have more fun saying or realistically because lighter hair catches the eye more easily in photographs. If you have naturally blonde hair, take your skin tone into consideration. Is your shade of blonde really doing you justice?
If you’re a brunette in an area where there are not a lot of blondes, you may consider going lighter. Find a colorist you trust and work gradually: you don’t want to be bleached and distraught with a color you have to spend loads to correct. Consider your skin tone and lighten gently—think golden honey colors rather than Barbie Doll yellow.
If you have naturally red hair, you’ll definitely be in demand and should consider boosting your natural color up a shade.
In general, you want your hair to look natural and striking—not fake and too put upon. Take a good, hard look at your skin tone and style, ask for opinions from those you trust, and then don’t be afraid to go a little bolder than what you’ve got.