Changing the underline color

Hi. I am noticing that in two different parts of one document the underlining color is different. I would like to understand what feature affects the underlining color and be able to modify it to be consistent. I can of course copy-paste into the same format that I want, but that would be a bit too roundabout.

I found an old thread about a related topic from 2015, but that did not explain the situation.