Here's why:
* Metaphor: A figure of speech where a word or phrase is applied to an object or action to which it is not literally applicable. It creates an implicit comparison.
In this case, "plumage" (which refers to feathers) is being used to describe "portion" (which refers to a part or share). This is a metaphorical comparison, implying that the portion is as colorful or decorative as feathers.
It's worth noting that the phrase is likely nonsensical on its own. It might be used in a larger context where the metaphorical meaning is clear.