This is historically correct. Morning dress always allowed for flair in the waistcoat. Bear in mind that until 1920, fancy waistcoats were common with frock and morning coats. Here's Lt. Commander Percy Silberston wearing a black lounge/stroller in 1954, as part of his wedding rig. The trousers are black and white houndstooth. Photo courtesy of Sator
. Is the vest flashy? Sure. Is it incorrect for morning dress? No. So there's nothing incorrect about a buff or cream vest with morning dress. You wouldn't wear one to a funeral, but it's perfectly correct morning dress for festive occasions.
Note the long watch fob dangling from his waistcoat (vest) - positively Regency!
Also, his trousers are not creased- very pre-1910.