First of all there are two major types of colored contacts - enhancement color lenses and opaque lenses. Enhancement lenses are suitable for people with light eyes only, and are designed to make your own color brighter or give it a slightly different hue. For example: a person with naturally green eyes can wear blue enhancement color lenses and get most beautiful aqua effect.
Opaque lenses are designed for a more dramatic change. Whether you have light or dark eyes, opaque lenses are not transparent, so they completely replace the natural color of your eyes with the color of the lens.
What type and color of colored lenses to select depends on the effect you want to achieve.
You want your eye color to get brighter, but you don't want to startle everybody who knows you with a different color
In this case, if you have light blue eyes, choose blue or aqua enhancement color contacts. You can also try Freshlook Radiance in Eden or Moonlight, which gives your eye an 'illuminated' effect.

If your natural color is gray or blue-gray, try blue from Acuvue 2 Colors or Freshlook Dimensions, to get a beautiful ocean blue color. If you feel more adventurous, go for jade green. Green eyes are quite rare, so you can make a statement with your new color.

If your eyes are brown, none of the enhancement color contacts would work for you. Try brown opaque lenses, which will make your color more defined, or hazel, which would make them lighter. You can also consider Freshlook Radiance Sunrise (lighter) or Autumn (darker), to add shimmer to your eyes.

See pictures of people wearing colored contacts at http://www.1-contact-lenses-consumer-guide.com/color-contacts.html

Do you want to try something dramatically different from your natural color?

In this case opaque color lenses like Freshlook Colorblends, Acuvue 2 Colors opaques or Illusions by Ciba Vision would be your best choice.

If you have dark eyes and dark hair, try blue or amethyst colors, like True Sapphire or Amethyst from Freshlook Colorblends collection. Amethyst looks extremely daring and sophisticated, because this color is very rare in nature. You can also try green color contacts; they would look especially good if your hair is red. For most people, green eyes are associated with sexiness and creativity.

If your eyes are naturally a cool blue or gray color, try honey color contacts. Honey eyes are associated with intelligence, warmth and trustworthiness. You can reinforce the warm effect by wearing warm colors.

Most people with dark skin naturally have brown eyes, so by selecting blue or green lenses you will attract a lot of attention.

See examples of colored contact lenses http://www.1-contact-lenses-consumer-guide.com/cheap-contact-lenses.html

To emphases the change, wear a new outfit, different in style and color from the clothes you usually wear. And to create a completely new image, change your hairstyle as well.

If you still not sure which color is best for you, ask your doctor to prescribe you disposable color lenses. Color contact lenses can be either annual replacement - you wear them for a year - or disposable - they come in boxes of six and you replace them every 2 weeks or every month. Disposable lenses are not very expensive - particularly if you buy them online - so you can try several different colors. The lenses mentioned in this article, Freshlook and Acuvue 2 Colors, are disposable color contact lenses.