Francophonie· easy
faire grise mine
“to make a grey face”
Meaning
to put on a gloomy, sulky expression
Explanation
Used when someone's face gives away that they're unhappy or put out about something.
Example
Il a fait grise mine en apprenant qu'il devait travailler ce week-end.
He pulled a face when he found out he had to work this weekend.
Origin
"Mine" is an old word for someone's facial expression, and grey had long stood for sadness and gloom in figurative French, much as it does in English.
Source