Aren't you saying the same thing that I did?
You asked why it was a bad idea to color code regs and I replied w/ ROYGBIV. I was just trying to answer your question. But I agree w/ you on the oxygen reg to id it on the surface. It is just a bad practice becuase the colors are meaningless at depth and just knowing that "oh, my blue one is my travel mix, but pink is a deco gas"... you can see where that is going. I would rather rely solely on proper cylinder marking.
And I would not O2 clean all of my regs, either. The first time you put non-O2 clean air through those things they are no longer clean. I will never breathe more than 40% on my back gas so they don't need to be O2 clean, and I travel a lot and run into a lot of different fill operations. Continuous blend or membrane nitrox? May not be o2- compatible air. Your regs aren't O2 clean anymore. I clean/store/handle my deco reg separely and when I start messing w/ multilpe deco gases, I'll just add to that group of regs.