Are you sure that you can distinguish between an unmarked police vehicle and an off duty officers private vehicle?
The following is available from the Roads and Maritime website:
Blue, or blue and red flashing lights are only be fitted to:
• Police vehicles.
• Ambulances solely used by the Ambulance Service of NSW
• Operational fire brigade vehicles.
• An RTA Traffic Commander or a Traffic Emergency Patroller
• State Emergency Service vehicles.
• Vehicles used by an accredited rescue unit
Blue and red flashing lights can only be used by a vehicle being used for police operational functions or urgent purposes.
This might be useful:
http://www.rms.nsw.gov.au/documents/roads/safety-rules/standards/vsi-08-flashing-lights-and-sirens-rev-4-1-nov-2010.pdf
