My starting colour image is of a market stall in the Rialto district of Venice:

colour

To do this exercise I applied a black and white selection layer over the file in Photoshop in the first I increased the red Chanel and decreased the yellow Chanel as you can see the red peppers are much lighter and the yellow much darker:
Red

Next i added a layer with the yellow increased and the red decreased giving the opposite effect as can be seen here:

Yellow

As can be seen the image has very different qualities, if I wanted a black and white rendering of this image I could carefully blend the channels to create the perfect image, notice how the red peppers blend into the garlic in the first version but the blackness of the red peppers in the second image provides separation between the two vegetables. By carefully controlling the chanels you can create an image where all the parts work with each other.