There is a new Google feature that we all need to get use

There is a new Google feature that we all need to get use to inside all their apps. How do you know if something is read or if someone is available?? The White card background= available/ unread. Gray card = read or unavailable. Gmail uses this on the mobile app. All unread email use a white card. When you read them they turn gray. The new Google+ desktop notification is great. It uses the Read vs unread or white and gray technique. Hangouts is the first app i noticed this in. On hangouts the user pic is white when they are available and the user pic is gray when they are unavailable / read. Expect this in other google apps from on now.