I think i understand what you are trying to say, that is when you read a topic it will appear faded and when a new reply is posted in that same topic it becomes bold to show that a new post has been made there. OP if this is what you meant then am sorry there is no way to stop it because so far as new replies keeps entering that topic it will always appear bold which signifies unread.
      After reading the replies of others and the solutions they offered but you weren't convinced, this is what i could think out since you said you don't receive notifications for new posts in your email because if you actually do, unwatching the topic here or unsubscribing directly from your email should have solved it.