so. this achievement thing

green-common 
blue-uncommon 
purple- rare 
yellow- special 
 
taken straight from diablo right?

don't remember purple in diablo.... in fact its grey, white, gold.

" green-common blue-uncommon purple- rare yellow- special  taken straight from WoW right? "

Yellow achievements? Whaaaat? Where?

Diablo:
 
White - Common
Blue - Magic
Yellow - Rare
Orange - Crafted
Green - Set
Gold - Unique 
 
WoW:
 
White - Common
Green - Uncommon
Blue - Rare
Purple - Epic
Orange - Legendary
 
 
So no. It's WoW.

I have not seen yellow.