What the Con System Means : EverQuest 2 Nerfed Info

Grey - Easier than "Green" - will not provide any XP or Loot
Green - Easier than "Blue" - Barely worth the effort, but still provides XP and Loot
Blue - Easier than "White" - Might be a challenge for 1 player, might not
White - Even encounter for player (generally)
Yellow - Harder than "White" - Challenging for 1 player
Orange - Harder than "Yellow" - Nearly impossible for 1 player
Crimson - Harder than "Orange" - Definitely Impossible for 1 player

To add more flavor, variable difficulty is introduced by the means of multiplying the attributes of each color-con by a set amount.

Example:

2 Arrows Down - a LOT easier than normal con, think "Peon" (zug-zug!)
1 Arrows Down - Easier than normal con, think "Henchman"
0 Arrows - Normal color con. No modifications.
1 Arrows Up - Harder than a normal con, think "Lieutenant"
2 Arrows Up - a LOT harder than a normal con, think "Mega Boss"
Now, the difficuly of this system, is that it is misleading somewhat.

a White ( - - ) con mob is not the same as a Green mob.
a White ( - ) con mob is not the same as an Blue mob.
a White ( + ) con mob is not the same as an Yellow mob.
a White ( + + ) con mob is not the same as an Orange mob.

Think of the ( - ) and ( + ) as meaning "x0.5" and "x2" in terms of levels.

a White ( - - ) mob will have a quarter the defence, hitpoints, and attack as a normal White mob.
a White ( - ) mob will have half the defence, hitpoints, and attack as a normal White mob.
a White ( + ) mob will have twice the defence, hitpoints, and attack as a normal White mob.
a White ( + + ) mob will have quadruple the defence, hitpoints, and attack as a normal White mob."

Old info.
Moving to Nerfed info board.