Pupslut said:
I don't know about green, but this search gets a few horse dicks:
disembodied_penis equine_penis solo -anthro -feral

The annoying thing is that I'm sure I saw that post a while ago. Having done a few more searches I'm guessing it just has the "penis" tag, and not "disembodied_penis" which would make it really awkward to find. I'll keep looking for a bit though.

A quick edit:
It could have been deleted, how long ago was it that you saw it?
adding "status:deleted" to that search gives four results.

none of the deleted images fit that description.

Well, one of them is greenish but it was Very Not Up To Art Standards, and didn't look very demonic.

Try penis_shot as well, though I don't imagine there's much there that yoru search didn't find.