The Green brand is for secondary storage, being reliable, cool and eco-friendly, whereas Blue ones are built for PC primary storage use. Other WD brand colours include Black for enthusiast products and Red for NAS and SOHO (small office, home office) use.
The Blue and Green SATA SSDs are designed to be used mainly in notebooks, PCs and workstations. The Blue product is optimized for multi-tasking and resource-heavy applications. Still, WD states that the Green SSDs deliver essential-class performance, and are a great option for every-day use.