While trying to mark all alerts and notices as read, I noticed that I was a bit confused which alerts or notices are read and which ones are unread.
In most other platforms, Phabricator, Facebook, Twitter, gray background for notification widgets usually signify unread notices, and the white background signifies read notices.
Is there a reason for this unusual design choice?
The idea was to emphasise unread notifications that are those you want to focus on. We are using a white background on unread notifications which provides higher contrast with the content. For read notifications, grey is used which is aligned with the way disabled controls such as input fields or buttons are represented when disabled to de-emphasise them. In addition, unread notifications are placed on top in the notification popup and they incorporate a blue dot to signal recent activity.
In the user research sessions we found no issues distinguishing read and unread notifications, but we'll keep an eye on this on future research sessions.
I see your point but as Pau says, because users are navigating this OK and it did fine in testing we see no need at this time to revisit. I'll put this in the Freeszer in case we want to bring it back some day for consideration.