I just wanted to pop in and say, great job for a first pixel
Now, your use of colors is... well, not to be mean, but it's boring.
Using Atnas's edit:
Do you see how his color choices are more interesting and dynamic than yours? That's because you don't change your hue much, just your saturation. That is, you add and take away grays in the palette, but you don't change the actual color. That makes it look, for lack of a better word, dirty.
This is what your color progression looks like in photoshop:
Look at the vertical slider on the right. It hardly moves up and down. That's what makes your colors look so boring. Not to mention the fact that they're far too unsaturated (grey).
Now, for the edit's:
You see how much the colors are changing? Watch the slider on the right. Also, see how the actual color picker on the left goes in an arch from lightest to darkest? That's what gives it a more interesting color.
And a little lesson, not everything needs to be outlined
Especially in black. I'd avoid outlining in black unless it's a stylistic thing.
