techniques to bring attention to one part of a line drawing?

[Mr Downtown]

I'm designing a color book that includes an old map, and I want to bring attention to a small central section—but not use something as obvious as a red arrow or circle. The caption mentions the feature, and I just want to make it easy to spot. The map is basic black & white, so I'm thinking of layering it with a color background that has a bright or light color under the (kind of circular) feature I want to highlight, and a more neutral color everywhere else.

I'm not sure what I should try in Photoshop to get the color "focus" layer. I was thinking I'd find a background on the Web that already had the focus, and layer it in, but I can't think of what to search for.