Last I checked, one did not need a diamond in their name to post questions tagged kolmogorov-complexity. I also didn't know that main site tags could be mods-only.
Oddly enough, when I'm in the editor it doesn't happen.
That's not a red tag; a red tag would have a red font on a pink background, like the tag below.
The copper font in your image indicates a visited link, meaning you have been to https://codegolf.stackexchange.com/questions/tagged/kolmogorov-complexity.