Here’s a still from the raw footage (DVCPROHD 1080i60):

And here’s the after shot, with only four very basic After Effects filters applied (click to embiggen):

I used Leave Color to keep just the blues and desaturate the rest of the image, then boosted the saturation a bit to make the remaining color really pop. After that it was just your basic Levels and a high-contrast instance of Curves.

Oh, and one extra layer on top as a vignette — a black solid with a rounded rectangle mask (double-click the mask tool to get one that fills the layer) set to subtract and heavily feathered. That’s all!

Leave Color has simple parameters but dramatic results, and is especially good as a quick trick if you need to draw a viewer’s eye to a key element of a scene. All you have to do is decide which color you want to keep. For example, say you have a shot of a bunch of people at a party, with one woman in a bright red dress. Choose that red with the eyedropper, then slide “Amount to Decolor” to 100%. Only the color of the dress will remain, and she instantly becomes the center of attention.

Sin City and Pleasantville (interesting combination of titles when you think about it…) are both good examples of how visually arresting color highlights can be on a black and white scene.