be shaded / be clouded / be blocked / be obscured

become shadow / be clouded / be obscured / get behind the clouds

become shady / go behind the clouds / be clouded / get behind the clouds

be shaded / darken / get dark / be in the shade

become shady / darken / get dark / be in the shade

become darker / get darker / become shady / be in the shade

become twilight / become dusky / (sun) go down

darken / become gloomy

become melancholy / (expression) become dark / (expression) become clouded / become gloomy

(countenance) darken / (countenance) become cloudy / become gloomy / become melancholy / become unhappy