The coloring in the quest log is an indicator of relative difficulty to your actual level in game.
Ie if you are level 10, quest level 8 and below green/grey 9-12 should be yellow 13-14 orange 15+ red.
This also indicates the amount of or lack of experience for killing the quest monsters and how much trouble you might have completing them solo.
Flashpoints are SWTORS "instances" if you are familiar with wow. the difficult is usually reflected bu the wording Heroic X + indicators
Mobs and rewards inside are considerably harder and better respectively than the usual world NPCS