Some additional discussion in T6393#80853. In general:

• I tend to agree that this is worth looking at adding additional emphasis to -- both for duplicates, and for closed tasks in general.
• As a concrete behavior, a fair number of users on this install subscribe to closed tasks. I'm not sure that this is a mistake, but we get enough of these that it seems like some of them are mistakes rather than users just, e.g., bookmarking the tasks.
• This is straghtforward to implement naively by throwing a banner at the top of the page, but a naive implementation will be inconsistent across applications (some will show banners on closed objects, others won't). Maniphest seems to be the major application where this is an issue, so maybe that's fine, but it's generally desirable to be consistent.
• Ponder will probably need a bold status treatment eventually, too.
• We don't actually denormalize or store what task a task was merged into right now. We'd need to start doing that before we could show "This task was merged into Txyz."
• Regardless of all that, we can give the "Merge" transaction bolder colors trivially.

We could also do something like:

Only this would be extremely helpful, thank you.

Now... have you considered an equivalent black background treatment at the "Closed, Resolved", "Closed, Merged" under the title?

We intend the header to be consistent across all Phabricator applications. While an open installation of Maniphest likely benefits from a more dramatic treatment, it doesn't make sense everywhere to me.

Ok, thank you! Something is something and this might be enough. I will report back if there is anything relevant.