That might be location dependent. Around here, green definitely does not mean nitrox.
I've never seen a diver with a green reg and have dove with a large number of recreational nitrox divers.
As well, around here, don't count on yellow for an octo, though yellow is often the colour of the octo. Could be any colour. Could be the diver donates the reg from their mouth. Best covered in the pre-dive plan.
Don't count on regulator colour to mean anything. Ask.
:scubadive
