Pretty good first try...
The color changing doesn't make any sense to me. It's a little slow, and I would have liked a little more precise shielding. Maybe something with masking or bitmap data. But an very nice first try, it didn't hold my interest enough to keep me playing very long though. What about adding power-ups or something so it's not just another space invaders clone? Practice makes perfect so keep at it, the graphics were nice and after you get a little more proficent you can expect some good ratings.