Nice Concept, Almost Nicely Carried Out
Nice concept indeed. I liked the retro feel to it, first of all. The sounds fit the "retroness" of it. The title page was good and simple. The game itself could use some work.
First of all, it would be better if the color changes were more in sync with the music. Also, rather than the arrow keys, with a game like this, it's better to use something in a line. Look at your keyboard. What about an asdf? Or even better.. dfjk? It just feels better, and there is no lag when switching. Speaking of lag...
When I switch from one color to another, I lose a little health in the process. There should be a half second amnesty from health loss to allow me time to switch from one color to another.
I wish there were more sounds, with each key press as well as throughout the game. Maybe a guy who goes "Nice!" or "Great job!" like in music themed games? How about lights and more color?
To keep someone playing a game, try adding checkpoints, more songs, or a boss at the end. Anything to keep the player... playing.
Anyway, that's my constructive criticism. I hope you use some of it. Overall, nice game, don't stop creating. (There was this one guy on Newgrounds who took criticism negatively and wrote a long, pathetic retirement letter and left Flash for good. Don't end up like him.)