As far as I understand it, the 2.1 (and other numbers) refers to the fastening system.
I have two set of Ortliebs, the older Classics with the older fastening system and a newer set with a newer fastening system. Both work fine.
However, the newer set used a different material not the heavy duty plastic/PVC of the classics and is nowhere near as robust as the originals nor as waterproof.
I don't use the inserts that Ortlieb supply to accommodate different rack diameters preferring to use hose on the rack. It gives a better contact and means I can easily swap panniers to different racks/bikes.
For heavy duty use it is worth considering replacing the bolts & caps Ortlieb use with metal or alternatively keep a good eye that the fastenings (bag to fastening system) doesn't come loose. I stress that's for heavy duty use.
Great bags, very versatile and repairable if the worst comes to the worst.
As for colour? Whatever is the cheapest