How can I get an effect like the blue in this image?
Here's the Photoshop (CS6) formula I used...
Black and white layer with "High Contrast Red Filter" selected.
Color balance filter. You have to play with this a bit, but:
Brightness/Contrast layer with an increase in brightness and reduction in contrast. Play around to get desired effect.
Curves cross process selection and adjusted opacity to taste using the luminosity blend mode. Experiment with the blend mode, you may find better options depending on the image.
The overall work is split toning, but with some added pieces in to it. Not a perfect match for what you did, various subjects and surfaces will matter here, but here's the result I got to with a little work:
Play around a lot more with the settings layer order and use masking to get even closer to the output, especially on the skin.
(instructions here for CS4)
Start with a fairly contrasty mono (or the whotes don't show through), this works well with non-destructive processes.
...and adjust to taste.
Edit:- here's the pic I was going to post. Could probably do with being a bit lighter in the mono conversion but hopefully it gives you the idea - full whites are white, blacks are black, midtones are tinted.