I am just using black, a gray, and white.

Actually, I am almost complete my game... other than music.
Oh, and, on that page, it said that the resolution cannot be larger than 640 by 200. Does this matter, or can we make the resolution larger?
EDIT: Heres my game,
PIXELRUNNER.
Play on YoyoGamesDownload from Will host for foodScreenshotHow to play:
Stay alive for as long as possible. Use the arrow keys to move, hold Z to use a Power Blast.
To stay alive: Avoid running out of the room, or being hit by spikes, wall spikes, planes, etc.
Hopefully I followed all the rules. I used three colours (Black, Light Gray, White), screen resolution 640 by 480.
Took me about 2 and a half to 3 and a half hours.