There is no regulatory need for the wiring to be red, though by convention it usually is, and it certainly should be something unique so as to be not easily confused with the normal wiring.

I am not aware of anything about containment, but the same principles about avoiding mistaken identity should apply  - after all  you did not paint the galvanized metal red I assume, but equally it was not shared with or looking like something else !

More generally PVC is not great in a fire, and burns quite hot and gives off nasty vapours and leaves a conductive char - while permitted,  its not a great choice for containing alarm cables.

There are white plastics that look like but are not actually PVC, though some are a bit less forgiving of the drill bit, and need a change of technique.

Mike.

PS

While not in the UK I have seen colour spots and bands used at the ends of containment to ident things where there is scope for ambiguity and opening the wrong one.  - there is no such obligation here, but labels or some scheme like that can be helpful.

According to the Electrician’s Guide, fire system cables should be uniformly colored but distinct from the general electrical installation cables. The recommended color for fire system cables is red. Additionally, using separate fire-resistant cables, conduits, and trunking or metal partitions is advisable to ensure proper segregation.

Thanks AMK. However, I am only interested in the plastic conduit colour as we always use red FP200 cable for fire alarm systems anyway.

Systems I’ve come across use white plastic  25mm conduit with metallic white saddles. 

This is exactly what I was planning to use but needed some confirmation first. Thanks AMK