Finding the perfect colored contacts for each person is going to vary. It depends on a lot of factors such as likes/dislikes, color of their eyes, whether or not they need vision correction, if they have worn contacts before, and what they want the colored contacts for. If you have dark eyes, going with the darker contacts will usually do a better job. I don’t mean darker contacts in the sense of colors, but more of tint. It really helps if you know someone that has the same colored eyes as you, or close, and if they have used colored contacts before. You can find pretty decent charts online of the different shades and how they will affect your eye color.
Going with blue contacts or green contacts would be the most common route, but during the Halloween season and before it, you will find that the colors of unusual shades really get a lot more popular. If you want to be a perfect vampire then no doubt will having awesome black or silver contacts would make a huge difference. It’s not that hard to match up with your favorite movie character, whether or not you will decide to use them for good or evil zombie contacts if up to you however!
Ultimately, most people just buy a pair after a little research and live and learn. This isn’t the best system, but it’s definitely a fairly quick way to find out what you like, and you might get lucky and your first pair is perfect. If you are going for extended wear, every day green or blue contacts, you might have to try a few times. They usually don’t do returns so make sure you at least get some use out of them.