OMG. Who can explain what all those monobook symbols mean, so we can work around them?

It's pretty simple: green is unseen. Both the arrows and squares turn green if the entry is unseen.

@Pginer-WMF can you please figure out how we should best fix this monobook system? Should we just override it, for example? Or do we need to adapt it?

In T176254#3636114, @jmatazzoni wrote:

@Pginer-WMF can you please figure out how we should best fix this monobook system? Should we just override it, for example? Or do we need to adapt it?

It depends on how much we want to support the seen/unseen distinction and keep backwards compatibility. Here are some options depending on that:

• Remove the additional marks. With the new filtering system, users can filter and highlight seen/unseen changes which was not possible before. We can keep their override for showing unseen elements in bold if needed (although I'm a bit confused on the use of bold since it has been considered too prominent in other cases).
• Keep the marks in general, but remove them when they conflict with highlight. That would make the system to be backwards compatible (users will see the marks they are used to), and these will only be removed when a new feature that also relies on marks is used. However, i find it a bit strange that different skins provide different functionality beyond just changing the styling and layout.
• Support the same kind of marks we do on the Watchlist. For the Watchlist we have a similar case of surfacing the seen/unseen information in a way that is compatible with highlighting. That's what I would recommend if we were aiming to surface the seen/unseen status in general, but given that it is a specific customisation on one skin I'm not sure it is worth moving those users through the change.