Duotone Effect
A duotone is a black and white image with an extra color added for effect. It's a feature that has been in Adobe Photoshop CC for many, many years. In fact, duotones have been popular with photographers when publishing high-end books of mostly black and white images. The Italian printing industry has one of the best reputations for producing such books, although now you can make your own with Elements. But this feature doesn't just stop at converting to black and white then adding color (which I guess is why it's called Duotone Effect and not just "duotone"). You can apply a gradient to the Duotone Effect, customize the color content of the duotone—in fact, you can have a lot of fun creating color images like never before.