Update 2022/09/13: A fix for this issue has been released.
The tag and username colors are an issue with accessibility-related color changes on post summaries. Everything within an ignored post summary should be grayscale with the exception of post status badges (e.g. "Deleted") and user avatars.
Expect a fix to ship in the next couple days. Sorry for the trouble and thank you for catching this!
The gritty details
Before recent accessibility-related color changes, we'd make elements within ignored and deleted post summaries grayscale with the CSS property
filter: grayscale(100%);. We were targeting any and all elements this way (with an exception for some badges). This was the easy way to do it since we didn't need to override the styling of each element individually, but it was a blunt instrument and resulted in poor contrast for many elements and an overall lack of control over color values.
We're now applying specific colors (grayscale color values) for elements within ignored and deleted post summaries. This way we can make sure that all elements within these post summaries have ample contrast and consistent, chosen colors. The drawback is that we need to be more thorough when considering any specific element that can exist within these post summaries and apply additional CSS rules to style them appropriately, especially in cases where Stack Overflow and network sites diverge from what is intended by the design system. It's more difficult to develop but, regressions withstanding, results in improved accessibility and gives our designers more fine grained control over these color values.