Satin is a browser extension that allows you to map specific colors in a PDF file to other colors. The default settings toggle to a "dark mode" where white is changed to a dark grey and black is changed to a light grey instead of a direct high-contrast inversion most extensions offer. This also retains the original coloring for images and diagrams, unlike a full inversion.
https://addons.mozilla.org/en-US/firefox/addon/satin-reader/
https://chromewebstore.google.com/detail/cplhiegcphlcgpmnbkfihbkgkminghke
Satin Reader reads the contents of PDFs you ask it to recolor. It also saves any custom colors you choose per PDF. All of this processing and storage happens entirely locally on your device.