Regarding someone else posting in green, we have taken note. And I agree, it could be misleading. So far common sense worked fine that nobody would use the green for normal posts, but we haven't explicitly said that the green is off-limits, or we might just as well remove it from the list of available colors.
As someone who is not a fan of too many rules and restrictions, I think common sense will prevail and this won't be a big issue.
Of course, if everyone started posting in green now (please don't...
), then we would have to reconsider.