[StudioJ]

Hey ST, (or anyone else for that matter) -- First you need to convert your images to greyscale, not just desaturate them but after you have converted them (channel mixer, desaturate, custom method) you need to go to (Photoshop) Image > Mode > Greyscale and then Image > Mode > Duotone. Once you have done that you can choose from the selection of built in Pantones, Grey/Black or Process tones in either duo, tri or quadtone and either use them as they are or adjust the colours and curves to suit yourself.

I tend to avoid the green based tones for any work on people as it tends to make them look sick. CMYK Warm looks quite good and I use it quite a bit.