OP
davesparks
your not supposed to use black as N anymore so that diy'ers dont connect phase to N
unless its re-using old wiring
Says who? Where does this 'supposed to' come from?
You can use whatever colour you like as long as it is correctly marked by either colour or alphanumeric marking at each termination.
There is however a strong convention to use the same cores of a three core as were used prior to the change and it is best practice to follow this convention.