I was watching The Sea Hawk
with Errol Flynn the other day and was surprised when the tint of the movie changed partway through.
When the movie is set in and around England and the England Channel, the b/w images are in shades of gray. But when the plot shifts to scorching jungles of South American and a quest for Aztec gold, the scenes take on a bright yellow tint--and then reverts to gray tones when the plot returns to England.
An interesting effect.