Wall lights - wall wires gray - which is Neutral and which is Live?

Hi there

I am installing new wall lights in the living room.
There is a green and yellow wire (which I know is earth), but the other two wires are both grey. How do I tell which is live and which is neutral?

Thanks

Is there an inner core to the grey pvc which show red/black or blue/brown?

If not the use a phase tester to determine.

ninsaga