Wiring a commercial fire alarm system using soft skin fire proof cable (aka FP200 etc) with core colours of brown and blue, my question is where does a fire alarm system fit within table 51 in the regs book, I would assume it is classified as a control circuit so brown and blue core colours are ok, but brown and blue would not comply if a fire alarm system is classified as a DC circuit.

If wiring with mineral insulated metal sheathed cable (aka pyro) you are free to colour the cores as required but as above what is required under the wiring regs and table 51.