The Userscript Tour
Invert the colour of the page
Userscript location:
https://en.wikipedia.org/w/index.php?title=User:BrandonXLF/Invert.js
This user script, present on English Wikipedia, does the following:
1. Adds an Invert link to the top toolbar.
2. Allows to invert the page colour and the colour of images.