Also you should note that your work should be enough different from your source of inspiration (sprite edits for example don't allowed here, so you have to figure some new features to distinguish it),  be good enough on it's own and there's a guideline not to use white background because it's very bright to look at.

Ah, thank you very much.

I was wondering why it was looking a bit jagged when I zoomed back out to 100%. I'm quite new to this, so this is a learning experience as I go along.

If you study Code Monkeys more carefully, you'll see that

1. When they use outline, in most cases they are one pixel wide. see 'clean lines' here:

http://www.pixeljoint.com/forum/forum_posts.asp?TID=5692

2. They use more saturated, more 'colourful' colors. You should always try to pick your own but if you stuck, you can use color choices from sites like

http://www.colourlovers.com/forums/1,2,1210/%5B_Rate_the_Palette_above_you_%5D?page=2

or pick colors from some oldschool game.