Interestingly, I've been thinking lately that I need to use the duotone options on my camera more, and then I saw this article at Light Stalking with a list of excellent examples. Duotone has an official definition, but it's easy to think of it as black and white photography with an extra color added in. Typically this extra color is blue, red, yellow, or green.
When it snowed on Christmas Eve (yay!) I traipsed outside to do a little snow photography. A regular B&W photo is first, so you can see the difference duotone makes:
In my camera's menu there's a Picture Control subfolder, inside of which I can choose Monochrome and then tap into a variety of options, including toning. What's nice is that besides having seven or eight hues to choose from (including purple!), I can choose how saturated I want them to be, from the barest hint to um-that's-not-really-what-you'd-call-professional.
I'm ready for bleak days and misty mornings, snowfalls and post-rain showers so I can practice duotone some more. :)