from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Of or pertaining to working-class professions that do not involve significant manual labor, such as skilled technical professions, combining elements of blue-collar and white-collar.
From gray and collar by extension of white-collar and blue-collar, perhaps with gray being seen as intermediate between white and blue. (Wiktionary)
"Traditionally, that was true, but for blue-collar and gray-collar [maintenance and custodial] jobs, the wages are now about the same in both sectors," he said.