Ability to automatically dim secondary monitor when focus on primary

Question

Is there a 3rd party app or combination of system settings and scripts that dims a secondary monitor until focus is brought to a window displayed on it? I like having multiple monitors but I would work better if there were a strong contrast between the two, where the contrast would invert based on which monitor had focus. (I can and do manually adjust the brightness when I know I won't need anything on the secondary monitor for awhile).

Running El Capitan with primary of a Thunderbolt display and secondary of a Macbook Pro.

I have looked at questions such as Show a screensaver on a secondary display and Adjust brightness of secondary display and have a sense that some of the tools might, with a additional scripting, get me close to what I'm looking for, but I am hoping someone has already solved this specific issue.

This doesn't answer my question, but this very simple work around found here Can I change the brightness on a secondary display? should help me out a lot.
If you press Control-F1 or Control-F2 the brightness on a secondary display will adjust. — bullcitydave, Apr 27 '16 at 17:19

score 0 · Accepted Answer · answered Sep 07 '16 at 14:47

I started using the free app HazeOver which dims all windows other than the one with focus. The new beta version has a preference to dim all windows on a secondary monitor, and it gives me exactly the functionality I need. You can also opt to not dim windows that belong to the app in focus. (I paid for it, which just removes messages encouraging you to purchase it).

Ability to automatically dim secondary monitor when focus on primary

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