Colours are sorted according to the following:
Important interrupt - Magenta (pink)
Fear caster - Warlock/purple
Healer - Lime (green)
Cone attack/whirlwind type of abilities - Warrior/Brown
Ranged - Hunter /green (Crossbowman on second boss in NEcrotic wake - take boss to this guy)
Fixating npc - Orange
Heavy AoE Damage - Maroon (dark Red)
Kill first type of add - Gold
Rage dispel - Aqua (light blue)