Go to Layer → New Adjustment Layer → Curves and switch from RGB to Reds. Then drag the line downwards a little for the shadows and upwards for the highlights, creating a slight “S” curve. Do the same for the Greens. For the Blues, drag the highlights down a little and the shadows up (for an inverted S shape). The shadows should now be slightly blue-ish, the highlights slightly yellow-is. Create a new layer with Shift + Control/Command + N, and fill it with #000066 (RGB 0, 0, 102).
Set the blending mode to “Exclusion.” Now copy the background layer by clicking it and pressing Control/Command + J. Set the blending mode for this copy to “Soft Light.” To decrease the effect overall, activate the top-most layer and then click on the background copy while holding the Shift key, thereby selecting both layers. Alternatively, you can add them to a group with Control/Command + G. Reduce the layer’s (or group’s) opacity.
Note that in Photoshop versions prior to CS5, you’ll have to reduce the opacity for each layer individually. If you’re ambitious with your collages, then you’ll be familiar with this problem: meaningful layer names are often neglected during the creative process. This can result in layer names like “Layer 4” and “Layer 5 Copy 2,” which are not very helpful when you need to quickly identify the contents of a layer.
Photoshop offers a number of solutions for our laziness. For example, you can click on the element you want to select by using the “Move tool” and holding the right mouse key; you’ll see which layer contents are below the tool. Photoshop will display a list in a drop-down menu, from which you can easily select the desired element.