Z1: Left image.

Z2: Right image.

Z1's red moved to Z2.

Z1's green moved to Z2.

Z1's blue moved to Z2. Note absence of depth.

Z1's red moved to Z2, Z2's blue moved to Z2's green.

Z1's red moved to Z2, Z2's green moved to Z2's blue.

Z1's red moved to Z2, Z2's blue and green averaged.

Monochrome: Z1 and Z2 converted to greyscale and moved to blank image's red and blue/green channels.

Same as first version except this experimental Photoshop action has been added to both images beforehand to desaturate pure reds and blues. If you come up with a better one please email me.

AJKelly's method: both images' saturation raised to 60 in Hue/Saturation, Z1's red output level zeroed in Levels, Z2's green output level zeroed in Levels, both resulting images moved to separate layers in new document and top layer's mode changed from Normal to Screen.