Objective Difficulty Color Coding

WOW has a system of color coding that can help you know your skill level relative to a quest or task: red, orange, yellow, green, and gray.  (There is another, slightly different color system for items you loot or craft.)

The color of a quest in your log represents its difficulty relative to your level.

RED means no.  You can't get any red quests.  You can"t gather items that show up red when you run your tooltip over them, even if it is your chosen profession.   If you select a mob and its level number is in red, you have to be skilled to take it out. 

ORANGE means good but dangerous.  You get high experience points (XP) relative to your level for completing orange quests and for orange-level tasks in your chosen profession.

YELLOW means just right.  You should be able to do any yellow quest, even if you are mobbed a bit.  Yellow gives you decent XP and when you craft a yellow item, you usually (but not always) gain a point in your profession.

GREEN means easy and low XP.  In every region you quest, if you enter at orange, the quests will be green or gray if you do every quest there.  You will level slowly and gain very little in your profession.  Move on.

GRAY means zero.  No XP.  No value gained for making an item. No point except that the quests may also give you reputation.  There are various ways of gaining reputation. Don't worry about that now.

Your quest log shows the quests in one of four colors.  When you select that quest, the bar highlighting it will also be in that color.  Similarly, when you open your crafting profession window, the items you can craft are listed in the same four colors.  (There are only 4 colors because you cannot get a quest or learn a skill in your profession at the red level.)

The wolf's level number is gray meaning the level is too to give XP.

These colors show up in all kinds of places and relate to experience and skill.  On the red end of the spectrum, the experience you get for any completed action like killing mobs is highest.  That diminishes until you hit gray where you get zip, zero, no levels at all. The only reason to do gray quests is for the reputation they give with a city or faction.  That can get you valuable rewards, but you shouldn't worry about that now.  Know that as you level, quests you have accepted change color, and you should abandon them once they are green or certainly gray.  You will not even see any gold exclamation marks offering you new low quests unless you turn on low level quests in the objectives
menu.

Knowing what the five colors mean can make your game play easier and more fun. It can save you from getting repeatedly mobbed and killed, from going out of your way to farm a mineral or herb only to realize your level is not high enough, or for grinding and grinding quests as you wonder why you are not leveling.