Hey, thanks for playing. I'm glad you enjoyed it.
As for the shields, it's not a bug - there are available 7 colors in total - every time there are 6 shields, each one of different color - the player's task is to use the "7th" color which isn't present in enemy shields. So basically every turn there is only one correct color you can use to hit enemy. Unless I misunderstood you and there is some bug I don't know about. Anyways, thanks for pointing out, I will clarify that in game's description.