I have done further research and this is what I have found relating to No 93 and as mine is in for a refit, I think I am going to follow this colour scheme.

Fitting Colour
Hull sides Medium Admiralty Grey
Hull bottom Red oxide antifouling
Deck Matt medium grey
Cabin sides White (some evidence suggests a very pale blue-grey)
Cabin roof White
Cockpit coamings White
Hatch covers Grey to match deck
Foam monitors (2) Gloss signal red
Monitor nozzles Aluminium or polished brass
Fire main pipework Gloss red
Breeches connection Red body, aluminium handwheels
Searchlight body Aluminium/silver
Searchlight cradle Grey
Loud hailer Aluminium
Mast White
Mast fittings Aluminium
Navigation lights Black body with red/green lenses
Anchor Matt black
Anchor chain Blackened steel
Chain pipe Black
Bollards Satin black
Cleats Satin black
Fairleads Satin black
Towing hook Black
Chafing plate Steel/silver
Davit White
Lifebuoys White with four red bands
Horn Aluminium
Cowl ventilators White outside, black inside openings
Mushroom ventilators White
Gooseneck vents White
Fuel filler caps Brass
Rudders Bronze/brass
Propeller shafts Bronze
Propellers Polished brass
Rudder tillers Black
Window frames Aluminium/silver
Windscreen wiper arms Silver
Clearview screen Aluminium frame with clear disc
Handrails Polished stainless steel or aluminium
Exhaust outlet Matt black inside
Flagstaff Varnished wood
Ensign staff socket Brass

Paint suggestions (Humbrol)
White – 34
Medium Grey – 64
Darker Admiralty Grey – 147 (alternative)
Gloss Red – 19
Satin Black – 85 (or Matt Black 33)
Aluminium – 56
Brass – 54
Bronze – 171 (Metalcote)

Regarding the discussion about Monitor colours in my opinion it is a possibility that they were grey we tried this when we produced the first VMW prototype kit twenty + years ago and it looked O.K. but the craft benefits from the introduction of a few brighter spots so we continued with red.
The Vents may also have been totally white.

When I was in the Fire Brigade, we had some world war 2 new/old stock water cannons, and they were red, we sent them to the Channel Islands to try and disperse the oil from theTorrey Canyon.
Fred

@EdW It's a great pity that there appear to be no colour photographs of either the RAF Crash Rescue Tenders, however there are a couple of B/W films of the 94 in action during sea trials where the foam monitors are seen being used to extinguishing a fire.
It's impossible to discern the likely true colour of the monitors from the footage so, like many others, I have opted for the colours that you state as they are, in my opinion, to be most likely.
Have a look at the Associated Press & Pathe films and draw your own conclusions!
Robbob

@EdW Yes that would have been animal protein foam, we used to call it Oxblood on the tankers that I sailed on . It stinks and is highly corrosive so you will need piping that can stand that corrosive property.

Contrary to common belief, these are not only water cannon, they are foam cannon as well. The foam was a smelly cream/yellow foam.
After some research, this is what I have found relating to the colour .
The Vosper fireboat, the foam cannon (monitor) was typically painted red, matching the rest of the vessel's firefighting equipment. The nozzle itself was often left in bare brass or bronze, and pipework could be either red or metallic depending on the period and refits. There wasn't a single universal paint scheme across all 63 ft Vospers, as many were modified.

Cannon body/monitor: Red
Nozzle: Brass/bronze (or gunmetal on later refits)
Handles/controls: Black or metallic steel

Cupronickel, copper–nickel (CuNi)
This material was a test sample for a naval component.
It’s a bit heavy to post but I am in North Oxfordshire if you want to pick it up it’s yours.

@PeterN I have got some CuNi, will take a picture of it tomorrow and post it, that will give you an idea

@Plivez I think they would have used CuNi piping for that and probably did not paint it to allow for visual inspection so I would leave the whole thing sort of weathered very slightly greenish copper colored
"Copper-nickel (CuNi) piping was developed in the 1930s. It was specifically formulated in response to a requirement by the British Navy for an improved material to handle seawater corrosion and erosion in naval ship condensers"

@DalekJ As does everyone as far as I’ve seen.

I have done mine red with brass nozzles