How do you disable Smart Invert or truly invert all of your screen colors? In previous macOS, when you used the Invert Colors feature (Preferences > Accessibility > Display > Invert Colors), all the colors on the screen would become inverted, including images, so a page like this one would look like this:



Note the image has blue tones and the rolling dice is black at the top

In recent macOS (I use Mojave), a feature called "Smart Invert" makes it now impossible to invert images on a webpage. 
The same page would now look like this:



Note how the dice and the image on the right have "normal" colors - and not the top left logo for some mysterious reason

How does one disable the so-called "Smart" part of the invert? 
It simply doesn't work for anyone trying to invert images, which a lot of people deal with very often, whether in the art world, historical research or any other photography-related fields. Besides, "Dark Mode" already does that.

How do I quickly invert images on my display?
I noticed the issue you were facing - it seems to happen on Safari. Have you thought about trying Firefox? It seems to not "Smart invert" on Firefox from what I can tell.

(I can't add a comment due to reputation).