Green great dragons cant exist

Natives (and some non-natives after a while!) can tell if something sounds off, even if they cant explain why. One of those things is adjetive order. They follow some rules that even people using english for all their lives are able to explain because it just sounds natural to them

This order is

quantity/number - quality/opinion - size - age - shape - color - place of origin - material - purpose NOUN

This is why there cant be any green great dragon, but only great green dragons

There seems to be some exceptions to this, like big bad wolf, but in my opinion, bad is not an opinion of what you think of the wolf, but part of the name, as in big bad-wolf :)