Now here's probably something very basic I'm missing... It may lead to some more complicated questions so I'll post it here.
But I'll start simple, here I'll try to explain:
if you overlap the enemy with the crosshair and shoot (hold down z) the enemy turns red (animation frame 1), if the crosshair is not overlapping then it goes back to green (animation frame 0). This works fine if you have one enemy instance, but if you have several on screen and shoot them all they all turn red even though the crosshair is not overlapping them.
If you don't know what I mean then I think it will become clear if you look at the capx here:
https://dl.dropboxusercontent.com/u/98471899/Scirra/crosshair.capx