If your nte is fed from an underground cable then there will be (usually) a
blue wire and a white wire connected to the screw terminals at the back,
could this be the blue wire you see?
The wire colours which attach to the front plate shouldnšt be blue, orange
and white in any case. They would be blue/white, white/blue and
orange/white. If the extension wiring is old the they might be blue, orange
and brown.
Alan.