i use red/black for power, but i've seen green white done quit allot, think its a colour consistency preference. i.e. days if 4 core (obviously no G/W) for contacts, 6 core for detectors, so you could maintain the more common 4 core red/black for zone feed out, yellow blue for the zone return on DP systems.
today eol means you can feed 3 detectors from an 8 core, commonly brown/orange would be to the furthest device or pab, but maintain green white as power.
before anyone shouts and hollers, and gets all snotty, its what i have seen - not what i do.