If the green is all you can get, you may want to set up to use it. I know you've heard that's a no-no, but if you get rid of your "gold" completely, the green will provide freeze protection and corrosion resistance.
The difference in "green" and orange/yellow coolants is the green uses silicates and other stuff as corrosion inhibitor. It's life is 30K or less also. If the green and gold mix, the acid used as corrosion inhibitor in the gold, will precipitate the silicates from the green, removing its corrosion resistance. And the precipitated silicates will end up in (your filter if you have) or your oil cooler.
If it's the only easy to get coolant, you really have no choice. Just make sure you completely remove ALL previous coolant first and change your coolant at 25 0r 30k.