lamont:
some DIR divers put a bright cover on their long hose and black cover on the bungee.
My guess is that these are divers who are relatively new to DIR, and haven't thought the whole gas-sharing thing through. Do they also put bright covers on all their stage and deco bottle regs? And when faced with the resulting array of multiple brightly colored regs to choose from, how does the OOG diver know which one to go for? For example, do they take the brightly colored stage reg from the mouth, or the brightly colored primary reg that is clipped off to the right D-ring?
I personally don't see the point of a different color cover, and I believe it actually telegraphs the wrong message about the donor's intentions on how to handle an OOG situation. It's almost as if they are expecting the OOG diver to make the decision of what reg to take ("see, it's the
bright one!"). In most cases, an OOG (possibly panicked) diver is in no position mentally to stop and think about that, which is why the donating diver has to take control of the situation. And if the donor is truly in control, then the reg color is going to be irrelevant.
As you stated, in an actual emergency you will either see the diver coming (and donate from your mouth), or if they approach you unseen and can't find the brightly colored reg fast enough, then they will take the reg out of your mouth anyway. Either way, they get the "right" one, so there's no compelling reason to use a different color cover, IMO.
On top of that, color perception changes with depth, so there's no telling what color the OOG diver will "see" when the time comes. For these and a host of other reasons, relying on some type of color-coding scheme to identify a reg is not considered DIR.