Snowclone is a neologism for a type of cliché and phrasal template originally defined as "a multi-use, customizable, instantly recognizable, time-worn, quoted or misquoted phrase or sentence that can be used in an entirely open array of different variants" wikipedia 
The phrase "gray is the new black" identifies change, and evolution in style of dress. But the structure of the phrase itself has become an element of linguistic evolution. A cliché, yes, but also a systematic way to speak of change or difference.