I had noticed after a Facebook update recently that their icons had changed to hollow icons. Upon first viewing it, my immediate response was “what the hell!”. They blended right in with the massive amounts of text surrounding them, messing up the hierarchy that they normally create (Assuming Facebook does, in fact, want you to comment and like other people’s posts)! Aside from just taking more time to process, I think hollow icons also tend to blend in with the background- at least in this case. Facebook, at least on my phone, has thankfully since changed back (it didn’t take long).