The reason for Tolkienβs mistake, since you ask, is that adjectives in English absolutely have to be in this order: opinion-size-age-shape-colour-origin-material-purpose Noun. So you can have a lovely little old rectangular green French silver whittling knife. But if you mess with that word order in the slightest youβll sound like a maniac. Itβs an odd thing that every English speaker uses that list, but almost none of us could write it out. And as size comes before colour, green great dragons canβt exist.
Excerpt from: The Elements of Eloquence: How to Turn the Perfect English Phrase by Mark Forsyth