What happens when you click on the tab? You should see your subscriptions on the right. When you go to another DU page, the tab should then be unhighlighted. You can unsubscribe there.

You must have accidentally subscribed to a forum or a user. When you click on a user's name or otherwise get to their profile, there is a red button there to subscribe to the user's Original Posts.

Likewise, when you click on a forum name, like the one at top here or on the left, you get the list of titles, replies, start times, and recs. There is a red button to subscribe to the forum.

while still being able to have subscriptions.

I subscribe to 6 forums, and I like seeing those on the far left of the page "Subscribed Forums" section, with the folders yellow for ones with new posts since the last time I checked. I like that feature very much, and is why I subscribe to those forums. But the "Subs" tab at the top being lit up 95% of the time I can definitely do without this annoying attention-grabber. It's like living in a yellow light district.