I think @ThePastaNebula just wanted opinions on the graphics. Looks nice to me. It should be fairly easy to re-skin the Flappy Bird project to use that sprite sheet.
I like the idea. What it looks like remains a more personal taste. Personally, I am reluctant to use many (bright) colors because in my opinion it quickly gets a bit messy. If I had to use a lot of colors I would keep the hue low and definitely not use a gradient unless you do this subtly and everywhere.