[The Saucepan Man]

This would imply that green had an original status of good, and was given a bad connotation by Morgoth

Was Eru's original plan (per HoME) that everything (Man, animals, plants, the whole kaboodle) would be undying? If not, Morgoth cannot have been responsible for all of the colour's negative connotations, as there would still have been death, and therefore decay, without him.