Well, i don't really know for sure, but probably moderators and anybody whose setting this up made zombie and vampire virus (Lol). Anybody who was infected by vampire will have a vampire as their bounty and their force color, oh yeah and gradients too. And anybody who was infected by the zombie will have a zombie as their bounty, force and gradients color.
We'll infected if we lose to someone who was already infected, you can easily find infected ones ingame, just check tourneys or any crowded servers. ;)
And Count's right, i saw people asked someone to decap them. :/