Step One
First thing I do when creating my layouts is fill the image with a color, I used #32536B for this tutorial...
Then create a new layer.... make a selection down one of the sides of the image then grab the gradient tool and create a gradient like below.

Step Two
Then  add a stroke and also a drop shadow to make it look a bit better.. look below....

Step Three
Now duplicate this layout...... by right click on this layer and going to duplicate.
Step Four
Then go to Edit >Transform>Flip horizontal then move it to the side that doesn't have one.
Step Five
Step Five
Now create a new layer off of the bg layer and fill it with a color. Keep in mind this is the color of the content area - the selection should go from the top to the bottom. I used #B4B4B4.

Here is what I came up with