There are two different kinds of colored contacts, sheer tinted ones to enhance light colored eyes, and ones that change dark colored eyes--these are the ones that have clear circles in the middle to go over your pupils. I think the trick is to not put anything dark over your pupil.
I have blue eyes but would love to try violet or light blue contacts. I've tried the tinted aqua ones, which were pretty but kind of fake looking.
If you're squeamish about putting your finger in your eyes, try this: close your eye and press your finger on the middle of your lid, then look to the side. Your eye moves but the lens is held in place by the pressure of your finger on your lid. When you open your eyes, your lens will be on the white part of your eye, which is easier to put your finger on then the colored part. You can put them in this way too. Just put the lens on the white part, close your eyes, and it will move to the colored part on its own.