Should each enemy flash separately from others? Or all enemies flash at once, synchronized?
If each enemy has its own flash cycle, then the easiest solution would be creating a single animation RED-BLUE-RED-BLUE-red-blue-red-blue-red-blue-red-blue, and loop it. Set speed=2 for the first four frames and speed=4 for remaining frames. No events will be required.
To get the current color use AnimationFrame%2 expression, if result=0, it's red, if result=1, it's blue.
Or you can make an animation with two frames RED-BLUE, looping, and run a timer for 2 seconds on each enemy. On timer change speed of the animation (make it faster or slower).
.
If all enemies should flash simultaneously (synchronized), then you can do this with global variables. Add a global variable CurrentColor (may be "red" or "blue"), set animation to this variable for all enemies, and also when a new enemy is created. Every 0.5 or 0.25 seconds toggle the value. Every 2 seconds toggle the speed.