nope....the color is to indicate the designed level of the quest compared to your own. So if a quest is below your level it is green (or gray if it is far beyond your level). when it is an your level it is yellow and further up it turns red. So it is just an indication for the level, not the difficulty or the reward. (although you get a smaller reward in xp for quests that are green and grey cause they are below your level and more xp for quests above your level)
as for the pvp related question.. I'll leave that to others..
nope....the color is to indicate the designed level of the quest compared to your own. So if a quest is below your level it is green (or gray if it is far beyond your level). when it is an your level it is yellow and further up it turns red. So it is just an indication for the level, not the difficulty or the reward. (although you get a smaller reward in xp for quests that are green and grey cause they are below your level and more xp for quests above your level)
as for the pvp related question.. I'll leave that to others..
I thought there was a +/- 5 levels where you got max XP. So green quests shouldn't have a XP reduction. White quests will have a XP reduction and red quests would also have a XP reduction.
I have seen many videos and posts about XP farming talking about this +/- 5 level max XP gain.
Green quests are below your leve(3-5 lvls i think) yellow are around the same lvl as you. once you go 5 lvls(iirc) above a quest it turns grey and you no longer earn exp from it. From the menu screen goto journal, then quests to find out which ones are main/guild/side