I neglected to mention in yesterday's post that green collar, blue collar, white collar, gold collar, pink collar, and grey collar are all considered exocentric compounds. In general, there are two main types of compound words, endocentric and exocentric.
Endocentric compounds are those where the rightmost constituent, called the grammatical head, is what defines the category of speech and the semantic interpretation of the word. For example, a barstool is a type of stool that is used at a bar.
Exocentric compounds (which have been the focus of much of my work in linguistics) are generally believed to not be definable by either constituent and are therefore said to be headless. For example, a jailbird is not a type of bird or a type of jail.
Because exocentric compounds are said to be headless and not definable by the words from which they are formed, they have long been considered semantically un-analyzable. In turn, this semantic un-analyzability results in the perceived lack of productivity of this type of compound.
I, however, believe that exocentric compounds can be both semantically analyzable (through the use of metaphor and other semantic operations) and productive --- just look at the number of compound words that have been added to the English lexicon based on the linguistic template of the compound word white collar.
As the topic of exocentric compounds is one of my favorites, I assure you there will be more on their semantic analyzability in the future.