|Icons for the current Facebook, previous Messenger, new Messenger and current Pages apps.|
The flat blue background colour has been replaced with a subtle graduated background.
iOS icons that use simple flat colour backgrounds might conform to purist graphic design principles, but increasingly look underwhelming and unfinished compared to the visually rich icons surrounding them. Facebook has historically used a very spare and minimalist aesthetic across all of its products; very appealing to engineers perhaps, but a little too severe for long periods of interaction. Their designers have been gradually softening that aesthetic across all user interfaces over the past year.
The right-angled corners of the rectangular speech bubble are now rounded corners. See above.
The light blue horizontal strip has been added along the base.
This is one of the distinctive shared visual elements uniting all of the icons in this family of apps.
The secondary speech bubble has been removed.
One might argue that using two bubbles better represents a conversation, but having just one still communicates the essence of a messaging product. Also only using one symbol matches the family look of the other Facebook icons better.
The default iOS curved highlight has been turned off.
Most third-party apps now omit this default feature. Only two apps on my home screen still include it.
So the obvious question is when will the primary Facebook app icon be updated? It is now the only app still retaining the original aesthetic. Presumably, they will update it’s icon when today’s tardy HTML5 version is eventually updated to a faster native iOS app.