I'm on Linux Mint 19.1 Cinnamon, so this solution is untested on version 18.2 (if you're even still using the same version twenty months later). I suspect this solution will work for any recent version of Cinnamon, however.
After some searching of my own, I came across a solution created by rnbdsh and released on Cinnamon's own extension site called Cinnamon-spices, the extension being Negate Window on Super+I.
You can download the extension from the above link and decompress it in
OR, you can use Cinnamon's own extension downloader by searching for "Extensions" in your Menu or System Settings. Once there, search for "color" or "negate" to find the extension (but not "invert").
(Not sure if the rest is necessary on version 18.2. The extension might work as is for you. But for me the extension would not load until I made a minor tweak.)
Once installed, I had to modify the extension's
metadata.json to add my version of Cinnamon to the list of accessible versions of Cinnamon the extension works on.
The command to find your Cinnamon version is:
My version returned as:
"4.0" (and its preceding comma and new line) to the list of acceptable versions I was able to use the built-in Extensions tool to enable the extension.
(I also customized the shortcut in
extension.js to my own liking. The option is clearly labeled at line six of the code.)
As a backup link, the extension is on github. I'm not a programmer, more of a dabbler, but I'm sure it wouldn't take much for someone with a github account to update the extension. Honestly, that's more than I'm willing to figure out how to do, but after seeing posts on multiple sites asking how to invert windows on Linux Mint Cinnamon, I thought I should at least share the solution I found (that rnbdsh created) with the world.