Greens are lower RPMs and some kind of intelligent 'throttle back power/electrical consumption' drives.
The Reds are supposedly beefed up with better drive mechanics that contend with Always On needs in our 28-hours-a-day/8-days-a-week world. There is also some electronics that deals with NAS-standards, too, with marketing promises of better reporting.
"How about just work?"
The Blues, the Blacks... it's sounds like some New Zealand vs. Irish footballers.
The densities are getting amazing. Dual-sided drives holding 2Tb each side. So a 4Tb platter. Three platters. That's my 12Tb drive right there!
What's the hold-up? $179 each... no steenkin' quantity limits either!