Hi,
Idle is the time from your last keyboard or mouse Input.
Away is just a message.
iChat can colour this red.
You can obviously add text as well.
Idle can be over-ridden if the Screen Saver kicks in before the Idle time is achieved (less than 5 mins)
So can Energy Saver if the Computer sleeps sooner.
If no setting is made to set to Away the Buddies will see you go Amber if they wait long enough.
Timings get shown. You rarely see less than Idle for 10mins unless you tweak your Idle time.
You Do Not see Idle Away messages in iChat.
However mousing over an Away buddy can reveal that they are also Idle and the time with the Info Pop up.
10:44 PM Saturday; September 19, 2009