I decided to go with a 16 color EGA palette, since that's what I played most of my childhood games with. It's tricky using a lisghtly awful palette and also make things stand out from the background, becasue you are tempted to use only the most pleasing of the colors.
I also did the game in a little over a day, but that's just because I scrapped my first idea, and sterted the new one on friday, reusing some code and sprites.
Mechanically I just had the idea of the player setting their own difficulty and getting scored based on that.