darken up
Upper Intermediate (B2)neutral
To quickly get darker in colour or shade.
"The sky darkened up in the east, and we knew the rain was coming fast."
Hear it in context

Art of Handwriting! - Live in the Nutmeg Tavern
Townsends · 19:09
it'll darken up again.

things i'm not buying this fall
Lizzie Phan · 3:17
If I want to darken up my blush,

Matrix Bullet Time Effect - Full After Effects Tutorial
Ignace Aleya · 16:09
And we can also add a curves effect to darken up everything.