The different colors that you see in the game mean tell you the rarity of an item! Green is the most Common and you can keep it for 30 days. Blue is Rare and you can hold onto it for 10 days. Purple is Epic and you can only keep it for 5 days. Orange is Legendary and you need to find a place to drop it in only 3 days. Red is Unique. Since there is only one of each Unique item in the game, you have to drop it within 2 days. So if you see a Red/Unique, Orange/Legendary or Purple/Epic item snatch it up before someone else does.
If you pick up a Red/Unique, Orange/Legendary or Purple/Epic item, you can share that feat with your friends on Facebook!