In this tutorial, a free lesson from the Pluralsight video course, Designing in Duotone in Photoshop by Pariah Burke (http://abbrv.it/vidPSDuotone), you will learn how to non-destructively convert any greyscale or full-color photograph to monotone, duotone, and tritone with any colors you can imagine.
This technique works with Photoshop CS6 and later (including all versions of Photoshop CC).