I was thinking more in the rec diving times, when those who dont have similar set-ups are diving with you, some need a bit of a clue as to which reg to grab (even if you discuss in pre-dive briefing). Also given the fact that most reg sets are sold with one yellow and one "other colour" faceplates, which would you rather a rec diver who is OOA grabbing - the one in your mouth that is or isnt yellow, or around your neck that is or isnt yellow (i know you donate the one on the 7ft hose you breathe off)? Most essentially untrained divers (ie those not used to the rig, but still certified) would go for the yellow one regardless of where it is. Before you scan that without reading it, let me reiterate - they would grab the yellow one most likely, you dont want them to grab the one around your neck - they wont get it all that far, so how would you set that one up to make it easiest for them? This is assuming they come up to you panicked (ie not thinking straight, fairly common - how many times do we hear about divers like that?) and take the reg from you - i would prefer that to be the one in my mouth on the long hose - therefore to do so they would like to see yellow and i happen to have one yellow ane one gray faceplate from my first reg set-up - guess which i will put on the donating reg??? Yes i could buy another faceplate, but i havent been to the dealers store in a while, been diving (getting other fills elsewhere) or on vacation instead. Of course a "trained" diver would know and have practiced this plenty of times, so in a technical dive they would know what they were doing most likely and colour wouldnt matter to them.