Get creative with monochrome conversions using the Hue/Saturation adjustment in Photoshop
Firstly, with your colour image open, go to the Layers palette and open the Hue/Saturation adjustment layer (from the black/white button). This will mean we can go back to the adjustment at a later date, or remove it completely.
In the adjustment’s menu tick the Colorize box. This gives your image one hue across shadows and highlights and through all subjects. The default colour here is purple.
By adjusting the Hue slider, various effects can be created for colourising your image. A Hue setting of 35-40 gives the sepia tone appearance. However, set this slider to around 200 and you have a cyan-blue tint over the black and white image.
With the desired colour set, move to the Saturation slider and lower this to 10 for a more subtle effect.