This is really good! It reminds me of the classic Asteroids, but with an interesting twist.
Sound are nice and crunchy, music is catchy.
In addition to switching between the different colors, your ship can also use thrusters to locomote (which I kept forgetting) and collect pickups to help you survive longer. And the color-coded opponents are not the only foes: there are also UFOs and chunks of rock to keep things fresh. Marvelous.
My only quibble is this: I'm not sure it makes sense that the turrets that can hit different colors are all on different sides of the ship. The result is that the front of the ship is at a different angle to the turret, depending on which color you are using... a bit disorienting. I appreciate, of course, that space is a disorienting place. :)