The Blue and Green notifications represent different things. You won't get both a Green and Blue notice for a single update process.
The Blue is a notification that an update has taken place, because you have the Program Settings, Update (Basic), Virus database set to Auto.
The Green is a notification that an update is available, if you have the Program Settings, Update (Basic), Program (or Virus database) set to Ask, e.g. it will check if an update is available and Ask you via the notification screen.
The default settings are Virus database = Auto and Program = Ask (because they are likely to be much larger). You won't get that if the update is set to auto, it will just get on with it and notify you that the update is complete (Blue)
So program updates are the only ones that would generate the Green notification and they aren't very frequent, though we have had a program update 4.8.1290 about a week ago (19/11/2008) and a minor tweak of that update 4.8.1296 very recently. Program updates are spread over 7 days to balance server load.
So you probably missed the green notice or ignored it, if your program version doesn't match that latest one 4,8,1296, do a manual program update, right click the avast 'a' icon, select Updating, Program Update.