A hairdresser once told me that the hair color you're born with is usually the correct color for you. However, when people aren't sure about a color change, the suggestion is to go a shade slightly lighter than what you presently have, and see how that looks. If you have very dark brown or black hair, sometimes some subtle red highlights look very nice (but I'd suggest a professional do this type of coloring for you). Rule of thumb in color is that often a little goes a long way.
Now, if you want to do something more fun and colorful, there are preparations (sprays, temporary wash-in colors, etc.) that will wash out in 1-2 washes. Perhaps that might be an option for you on certain occasions (a concert, party, etc.), versus doing something a bit more drastic, such as permanently adding in a more vivid color.