Computim wrote...
Only problem I have with that is it shows the shockwaves on the galactic scale, anything moving that fast save neutrinos would carry some kind of mass, takes us back to the Artillery Officer on Mass Effect 2 Citadel informing his probies that "THAT BULLET KEEPS GOING UNTIL IT HITS SOMETHING WITH THE FORCE OF A NUCLEAR EXPLOSION" (or whatever the exact wording was). That many explosions would be the equivalent of storm surge/tsunamis and destroy craziness... not to mention the citadel was 'one big mass relay'. It was right next to earth when it blew up lol.
As they are sent out by the mass relay, we can assume that the waves are travelling FTL. We also are aware that they can send communications via Mass Relay, these communcations do not have mass, however can travel FTL.
We can assume, then, that the colour of your sparkly whizz is merely representative of the massless wave form front which is hyper accellerated via mass relay (unexplained in the codex). It dissipates most likely due to the fact that as the wave spreads out it becomes more diffuse as is the case with standard wave harmonics, which is why each Relay needs to spread out the bubble.
Also, as I said, the destruction of the citadel doesn't need to be massive if it is an internal explosion caused by the shutting down of systems and huge amounts of energy being release as heat internally as the mass effect drive vents as it is shut down. Yes, it goes up in an explosion, but it doesn't need to be massive. Of course the falling debris from orbit will cause some damage on Earth, but I think they have enought destruction there not to be overly concerned at that.
The Slug from the Everest class Dreadnaught is 20kilo and accelerated to an appreciable fraction of the speed of light, it would most certainly impact with an impressive force (though not necessarily a visible explosion). As we know, the slugs are made to squash on impact to send out the force through the target but that is more likely going to be a shockwave than an explosion, kinetic energy as opposed to heat and light, but I let them have their fun in their epic space battles because they would look dull without explosions hitting kinetic barriers.
But the wave, most likely massless. Also, if travelling at FTL speeds would be unlikely to physically encounter anything as would basically be in a different phase to matter as otherwise Mass Relays wouldn't be able to function as stars, planets, asteroids and comets would be in the way occasionally.