Well, indirectly the colour does make a difference. The green ones generally will offer less XP than say an orange or red one, because the quests are lower level quests. This of course depends entirely on what the quest entails, be it a 'fed-ex' quest or an instance quest, so much factors in to the XP granted upon quest completion. :)

The colours usually are indicative of the highest level mob or NPC you will have to slay for the quest. From my observations; if the quest involves no killing, the colour is usually indicative of the mobs or NPCs in close proximity to your objective, in the above example: Southshore Guards.

Q u o t e:
For alliance?

Good point. :) It's Friday... not enough shinies this week...

*looks for donations*