Color+Isolation

In this picture, the Coke bottle has been kept in color while the rest of the image is black and white. This is meant to emphasize the subject, which is the Coke bottle. It's almost like a commercial emphasizing to drink Coke.

The little lion plushie is kept in color to emphasize that it is the subject on the black and white bed.

This image from my aunt's wedding is black and white, except for the groom's boutonniere is kept in blue. The blue of it is to emphasize happiness between the two of them, as well as optimism. Also, blue was the theme of the groom and groomsmen's suits.

Optimus Prime appears to be dead, due to the black and white. The Matrix of Leadership is kept in color to show that the spark of Autobots is still alive. This is meant to mimic Optimus Prime's death in the original Transformers: The Movie.