Updated for Dragonflight Season 2
Color rules:
Purple=bosses (or boss-like)
Blue=Mini Bosses, Lieutenant-types. Extremely Important Mobs
Red=Dangerous Mobs with frontals/aoe usually
Pink=Mobs with an important cast that you want to interrupt
Light Green=A bit like pink, also important, often a cast, or some kind of minor aoe, maybe needs stunning
Salmon=regular mobs, make them dead, but not really scary to dps (they might have tank busters still)
Orangish-Red=something…different..something to be aware of…like spawned totems, etc.