It depends on the country. In the US and Canada, white or grey are used for neutral, but in Australia, white is used for phase 2 in a multiphase system or for "switched active".
In the US, white could also be used as a switched wire (e.g. for lights) and sometimes black tape at the ends indicate this. In any case, before someone attempts to modify wiring, they should ensure power is switched off at the breaker panel, plus double check with a neon tester that power is definitely off for the circuit.
This Wikipedia guide shows the colours used in each country: