This is an awesome game. I completed the game and looked at the comments. I found someone saying that level six is impossible? I retried it, and won... Just wait until later! MWA HAHAHAHA!!! Oh yeah, if you want to know how to defeat blues easily, read on.
Just stockpile up ships. As soon as you send out ships, the blue will fire at you from somewhere else, effectively killing you. Once stockpiled, shoot only half your ships at the enemy using the button in the top-right corner. Good luck!