Recently, something has changed... somewhere... looking at the source here, clearly it's not here, but after a recent Chrome update, the text color for the icon badge has become something dark and unreadable instead of the lighter color. This extension is the only one that is having this issue for me. I'm not sure how this is happening, as I checked the browserAction.setBadgeText function in the Chrome docs, and it still does not support setting the text color (Firefox does, but all other browsers, including Chrome, does not). So ya, not sure how to explain that. It doesn't make the extension unusable, but it is inconvenient not being able to easily see the time remaining until refresh.

Screenshot showing auto-refresh, tampermonkey, and ublock origin icons all with badges, with the TM and UBO icons showing correct white badge text, and this showing dark. Note that while it looks very clear and readable in this image, it is nowhere near that readable on my actual screen.

Edit to add: Looks like this might be Chrome breakage, this is a possibly related issue:
https://support.google.com/chrome/thread/164964343/chrome-extensions-have-black-dark-box-and-text-for-notifications?hl=en
https://bugs.chromium.org/p/chromium/issues/detail?id=1321962

Supposedly this was fixed in a Chrome refresh that came out in the last couple of days (102.0.5005.115, which I have installed), and it would appear to be related to code that is attempting to auto adjust the badge text color to account for contrast with various badge backgrounds. Obviously, of course this is not fixed, and I'm not sure it will be fixed in 103 as this thread would seem to indicate, so you might want to adjust the background color to ensure that the contrast is usable. I will keep this thread updated whether this is still an issue when 103 eventually comes out, if it hasn't been addressed manually by then.