The perfect extension. It works automatically - it applies dominant color according to one selected in Windows. And doesn't demanding access to sensitive permissions to YOUR DATA.

Update review (2019-05): sometime ago, after one of Firefox updates, the start page in my Firefox automatically reversed background color from dark mode (which I prefer) to white. Now, despite I selected dark mode in Windows, your extention remains in white mode only.
Could you update your extension so that the dark mode is automatically (or manually) selected?