We are somewhat confusing two discourses here, Dick. Of course we all more or less consciously modify what we sing to make it more amenable to our performance, so that if we find a phrase that doesn't ring true we try to find an alternative which will make it more comfortable for us to sing. As I have said, I use 'Lincoln green', which I think it was in a version I remember from long-since. Your 'coat of green' would equally sound well - if one wants to specify what M was wearing, which most versions don't anyhow.

But that does not alter the fact that the phrase in question, whether or not it 'makes any sense', does occur in some collected and published versions of the ballad, so that the OP was doing quite a sensible thing to see if anyone could come up with an explanation of it whereby it might make some sense; and all those assertions that he couldn't have read it like that anywhere, and must have misremembered something else, were less than helpful.

~M~