When the picture is transparent it means that they are not looking at the conversation.. i.e on another window or tab. Kind of confusing on mobile as you have to trust they are online, but on the computer it is fine.
Nobilis should be easily playable -- it uses no dice, so you're just keeping track of resources. Never played 3rd edition myself. I loved the biblical epic-ness of 2nd and couldn't get into the shoujo anime of 3rd. I wish you luck though! Nobilis is pretty great regardless.