I think I noticed last week that Them! had its title in green even though the rest of the film was B&W. At least I think it was that movie.
The Vincent Price movie The Tingler
is mostly in b/w, except for a LSD-induced dream sequence in the middle--with bright red blood.
And, bizarrely, War of the Colossal Beast
(the sequel to The Amazing Colossal Man)
is b/w until the final minutes of the movie--when it inexplicably turns into color.
As I recall, there's also a brief color sequence near the end of Portrait of Jennie--
during the climatic storm scene.