Good but level progression too slow
While I admire the minimalist style and the simple idea, which ended up being more fun than I thought it would be, the game just got boring after awhile. I kept on wondering if I had ever gotten to the end of it. I had no indication of how close to death I was when I got damaged, no indication of when the arena might change again, no indication of anything at all. i was just shooting ships for ages waiting for something to happen.
But something would only happen after about 8 or so minutes, which is a *long* time to wait for a screen color change and faster enemies. I just ended it in the middle of the purple with 82 something something points because I had no confidence that you had any more tricks up your sleeve other than making the enemies move faster. When the music stopped in the middle of the blue I wasn't even sure if you had programmed anything else.
So it was pretty nice, but add some variety, huh? Spice things up a bit, keep it interesting and engaging, keep the game moving, Don't leave me hanging waiting for something more to happen.