Other forms: greener around the gills; greenest around the gills
If someone is green around the gills, they seem sick. They might be pale or a bit wobbly, or they might seem to have no appetite. They’re just not quite their usual self.
Green has been used to describe the complexion of a nauseous person since the 1300s, and gills was already an informal word for the lower part of the face in the 1600s. However, the phrase green around the gills, or green about the gills, only became common around 1800. Some say it was first used among sailors on old-fashioned ships that were easily tossed about by rough seas. Even seasoned sailors would turn pale from seasickness.