How to do a duotone with transparency?

In Photoshop, a duotone is an image for printing (not screen display) with black and one other colour ink. So black and red could be a duotone; the person running the printing press would add a bucket of special red ink for your project.

Otherwise, it isn't a duotone (for example for screen view, or printing on a desktop printer). Some creative people may use the duotone features to get the effect they want, then go back to their real colour space (Lab, RGB or CMYK) for the final result.

So, when you're making the transparency, the chances are you aren't using a duotone. If you were, not sure what you'd do: it depends on your deliverable, which must be one of EPS, DCS2 or duotone.

Nothing specific here. Juist a custom channel used as a layer mask and the faces then having been colored e.g. with a color overlay layer style. Have a look at the Channels palette and functions like Image --> Calculations.

Mylenium