What are the "six green ships" that visit the man who really runs the Galaxy?

Question

In Restaurant at the End of the Universe, Zarniwoop commandeers the Heart of Gold, and brings it (along with Zaphod Beeblebrox and Trillian) to visit the man who really runs the Galaxy. He's a hermit in a metal shack with some serious solipsism issues. We're told several times that there are six people who know who he is and how to get there:

On a small obscure world somewhere in the middle of nowhere in particular - nowhere, that is, that could ever be found, since it is protected by a vast field of unprobability to which only six men in this galaxy have a key - it was raining.

(Emphasis mine, all quotes in this question are from Chapter 28.) And these six men apparently all visit at once, and all have black ships:

“Fish come from far away,” he said, “or so I’m told. Or so I imagine I’m told. When the men come, or when in my mind the men come in their six black ships, do they come in your mind too? What do you see pussy?”

But when the big white Heart of Gold lands and he sees it, he says this:

“I think I saw another ship in the sky today,” he said at last. “A big white one. I’ve never seen a big white one, just the six black ones. And the six green ones. And the others who say they come from so far away. Never a big white one."

What are the green ships? And, for that matter, who are the others who come from far away? Or are these just another one of Douglas Adams's beloved red herrings?

Answer 1

In the radio series, only Black ships are mentioned, not Green.

The reference to other ships is to show that several races come for advice. Vogon ships are always described as yellow so it isn't them at this time.

Adams is hinting that the real rulers of Earth, even in our reality, are not the people you think they are. It is a nod to all the conspiracy theories about shadowy organisations.

Incidentally, I have always taken it that the Cat rules the universe. The man says that people always come to sing to the cat, and he calls the cat Lord.

Answer 2

The Green ships are the Betelgeuse Trading corps. Whenever Ford was caught staring at space, and asked why he was scanning the skies, he would answer that he was looking for green flying saucers. Altho he admits that any color ships would do, really.
"The reason he said green was that green was the traditional space livery of the Betelgeuse trading scouts."

Answer 3

The Black Ships were the fleet of the species with the most unstable genetic system in the Universe who regarded everyone else as "filthy dirty rotten sameling". Something like the Vlerherd?