Regarding green ("friendly") enemies: I think that it requires the "green" player to relog one or more times, and may require a complete exit from the client for this bug to go away. Convincing someone to relog/close the client, however, may be a tad bit difficult. If *you* are seen as "green", are informed of this by your opponent(s) and you have any sense of honor/ethics, relog.
Regarding green gates: On the plus side, relogging seems to fix the problem for the affected player. On the downside, if/when you relog, you will lose any merits, devices, and scrolls you have in your backpack. You will *also* lose any Library discounts and Forge/Lumber Yard buffs that have been generated. The same downsides apply if you relog to rid *yourself* of a "green" status.
See? Kermit was right!