Collocations for sombre - adj.

be, look, seem
Everyone looked very sombre.

become, grow, turn
His eyes grew sombre.
The mood turned sombre.

remain
The mood in the city remained sombre.

extremely, fairly, very, etc.
She was in a somewhat sombre mood.

suitably
The funeral cortège passed, to suitably sombre music.

Sombre/somber is used with these nouns:
colour, mood, note