William Marshall Cazalet John Singer Sargent (1856-1925)

The picture has something of this: people, wear, man, two, portrait, woman, mammal, outfit, cavalry, recreation, lid, veil, facial expression, group, outerwear, pants, seated, music.
Perhaps it’s a painting of a man in a red coat and white pants standing next to a brown horse in a wooded area with trees and bushes in the background.