Since there's so much confusion around this, I'll start off with a little background.
Frequented tags are an alternative to favorite tags which are automatically inferred from browsing patterns. If you have no favorite tags, questions with your frequented tags will be highlighted as if you had used the favorite tags feature.
This is a nice idea (and it's easily turned off if you don't like it), but it's confusing and poorly documented. Users are introduced to this feature by the sudden highlighting of questions which have their most frequented tags. This causes confusion:
- OK, I'll bite... why do some front page questions suddenly have backgrounds? They're lime green on SA. [In Teacher's Lounge]
- It sprung up on me in the middle of my browsing... one second, I had a page of white questions, and then on refresh a great fraction turned blue. [Please let users opt out of the “frequented tag” system].
- I am not able see all questions correctly, some rows are displaying in yellow, some are in white ... [Displaying weird in firefox (nighlty build)]
- I think there's even some automatic detection of your most active tags and those get auto-favorited (don't quote me on that). [Answer to "Displaying weird in firefox"]
- This is how Stack Overflow looks on my Opera browser as of today, note the background color: <image> I already tried upgrading Opera to version 11, but the issue remains. Is this a bug or a feature? [Why is Stack Overflow suddenly orange?]
- Starting a few minutes ago, questions tagged "etymology" are highlighted in blue when I visit german.sx. ... Is this a bug? EDIT: The hightlighting just disappeared all by itself. Nevertheless, I won't delete the question yet in case the phenomenon returns. [Why are “etymology” questions on german.sx highlighted for me?]
Note that this list is not intended to shame these users. Several of the authors discovered the cause and solution independently. I intended to use this list to demonstrate that this is a non-intuitive feature. It should be documented somewhere.
In my opinion, it should be documented in such a way that the documentation is presented to the user when the feature is first invoked. A dropdown to the effect of
frequented-tags has been detected as one of your frequented tags.
Questions with this tag will be highlighted to make them easier for you to focus on. More tags may be added based on your future browsing habits.
Alternatively, a better opt-out mechanism could be implemented. If that's done, post the answer to Grace Note's feature request.