Hi 4HP,
The Altitude Box is highlighted in white between 900ft and 300ft
when approaching a selected altitude. No aural alert well atleast not in our aircraft.
You will get an Eicas Caution >ALTITUDE ALERT with an aural beeper if the aircraft has deviated more than 300 ft from the MCP selected altitude. Also the Altitude Box changes to amber when deviating from selected altitude between 300 and 900ft.
Hope that helps
Cheers