Slight grey stroke around lines in illustrator

I just bought a wacom tablet and I'm attempting to familiarize myself with Adobe Illustrator. I'm learning how to color stuff in, and for some reason there's very noticeable grey around the edges of what are supposed to be completely black lines. I understand that this is pretty much how a computer gives off the illusion of a curve because we're dealing with pixels here. But this is extremely noticeable, it just looks horrible. I'm using Adobe Illustrator CS5. It would be amazing if somebody out there had a solution for this. I'm posting a screenshot of a quick drawing I did just to show what's going on. Look at the thin "black" lines, they are almost completely grey. If anybody out there has an answer, thanks in advance!