Quote Originally Posted by mklotz View Post
Sometimes these confusions can be resolved by appeal to the more obscure rules of grammar. If the two adjectives are coordinate adjectives, i.e., they both refer to the noun (as opposed to the first adjective acting as a modifier of the second adjective), they should be separated by a comma. The test here is to mentally replace the comma with "and". If that still conveys the same meaning, the adjectives are coordinate and a comma is needed.

Example: "An old teak door" could be written as "An old and teak door" so a comma is required → An old, teak door

Since "purple people eater" is written without a comma, and "purple and people eater" makes no sense because you can't eat a color, we have to assume the "purple" refers to "people" and not to "eater".

If one is a skilled writer, such confusing double adjective constructions will be caught during editing and reworded to unambiguously convey the intended meaning.
A skilled reader is as essential as a skilled writer. Yes the purple refers to the people. As he himself explains "...eating purple people and it sure is fine" "...I wouldn't eat you 'cause you're so tough."