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.