Somebody else who only gets green results while lying on their back (supine position)! I guess I'm not the only one. I can use my Aerobika and 7% saline twice a day religiously (and I do) and see nothing much, but miraculously when I do yoga, up comes this yucky stuff I had no idea was there. After an hour of yoga I can feel things loosen, then in the "corpse pose" at end (flat on back), it becomes apparent. Green color and quantity vary, but if it's been a while since my last yoga session, chances are I will produce this stuff. I see similar results if I lay on my back after a strenuous, warm bike ride. Of course, this takes even more time, but I guess this type of therapy is good for me in many ways.
I report all of this to my doc at NJH who also doesn't seem overly concerned, although it's clearly best to remove it from the airways, as able. The breathing techniques in yoga may also lend themselves to lung clearance.
I tried 12 hr timed release Guaifenisin (Mucinex ingredient) and ended up with lots of throat clearing. It didn't seem to help bring up green mucous during airway clearance.
Best to you in your journey...