External is usually where they want to approve the color of the house, types of materials, roofing, landscaping, driveway condition, etc.

I have seen doors swing wide open and shadowy-figures emerging from the darkness.

We want something neither light nor dark—maybe a mid-tone that won’t show too much wear.

You can try free sites like Spokeo as a shot in the dark, but it's not too hard to find the owner's information if you are good on the internet.

We use 2 wall colors for simplicity and ease of repair.

Case in point: LA city... and most recently, in the dark of night without warning, Pomona.I know there will be some on this forum who may disagree and will have their personal stories of how to overcome it and work around it.

I see lots of people with unrealistic rose colored proformas that I hope will be saved by an appreciating market. 

Unpopular opinion: throw some wood/floor colored caulk in the spaces and call it good. 

Are they picking window style and placement, exterior cladding, color, etc? 

First thing I would do is swap out the daylight color bulbs with a warmer tone.