It seems to me that you agree with Swizec. 'Great Dragon' sounds just like 'Great Dane' when you put other adjectives. Certainly to my mind it sounds like it's a particular species of dragon. Given that the only place green-coloured dragons live is in fantasy (the komodo isn't green), there's pretty free reign to interpret it.
And in the context of animals, it's particularly unusual to use the adjective 'great' by itself, without it being part of the breed name. 'Great big' maybe, but rarely just 'great'. If you saw a large bulldog, it would sound strange to call it a 'great bulldog' instead of a 'great big bulldog' or other adjective.
This being said, because of their most prominent colour, we can talk about "gray great white sharks", and get the colour in on both sides :)