Western Digital have dropped "Cavier" from their product names.
The colour represents then intended usage; Black for performance desktop, Green for power saving desktop, Blue for "value" desktop, Red for NAS and Purple for surveilance.
Seagate Barracuda 2TB (ST2000DM001) is a good all round drive for a computer, faster than the WD Green, cheaper and with lower power usage than the WD Black. These drives are not suitable for use in a NAS (Seagate has a different drive for this just like WD).