1- Advanced blending
- Duplicate the background layer Cmd+J Ctrl+J.
- Using Shift + ←, sligthly nudge the duplicate to the left.
- Right-click on the duplicate layer, and click on Blending Options.
- In the dialog that appears, and under the Advanced Blending option, uncheck the R (Red) channel.
- Now click on OK to confirm.
- Hit Cmd+T Ctrl+T to activate the transform tool and Shift + click, hold and drag out to slightly enlarge the duplicate.
- Use the Move Tool → V if needed to adjust the position of the duplicate layer.
- You may also want to crop your image slightly to the edge of the duplicate on the right side.
Et voilà. In basically just one step you have your double color exposure effect! You can play with turning on or off different color channels in the advanced blending options rather than the red one, and you can also play with the fill opacity and knockout mode to achieve different creative effects.