Thanks - always really nice to hear someone liked your creation! :)
That particular element was done in a really basic way: When a player takes a hit, a float value is set to 1. This value is then subtracted from the green and blue channels of the material making it fully red and gradually fading back to full colour as the value is reduced each update. I partly did it just for aesthetic reasons but thought it, combined with animation, really helped to make it clear who had just been hit. The other use I have for the same value is that it represents a brief invulnerability period to prevent getting absolutely hammered with no chance to break out.
Thanks again!