This is the second time that I've seen a question appear faded!
If I recall correctly, I have already seen another question like this. Why does this question appear faint?
You have probably put the tag in the Ignored
list in the main page.
More information about the favorite and ignored tags can be found here.
Quoting:
Favorite tags are meant to call out questions that are important or interesting to you. Any question tagged with one of your favorite tags will be highlighted on the homepage and questions lists.
Ignored tags downplay subjects you are not as interested in. Questions with these tags are faded on the homepage and questions list, but are still visible. If you want to completely hide questions with containing your ignored tags, you may checking the "Hide Ignored Tags" box in the "prefs" tab of your profile.