The point that El Tel makes about the roof and quarter panels
is correct...
The 454 body panels are made of GRP (Glass Reinforced Plastic),
they are a lot more flexible than the steel body panels of a 'mainstream'
mass produced vehicle, which makes them prone to damage by excessive
pressure that some use for jet washing. Most are operated by non UK
nationals, and no 'real' training is given to them, so one car is like any
other to them.
Most if not all of the jet wash operators appear to love getting 'up close
and personal' to the cars they clean...intent on blasting off every little
bit of dirt or marks that they see...like tar or slight scuffs, so the actual
area the water 'impacts' on is small and put under far too much pressure
which can and will distort and damage GRP panels !
So....my advice if you do take it to a hand wash establishment that uses
jet washers, is to tell the person 'waving the wand' to stand back further
than they would to metal bodied cars...even explaining why.
OK..so they may not comprehend exactly, and if such is the case then
find someone there who can explain it to them. I did, and they treat
my cars with 'respect' when I turn up and want any of my Smarts done.
Jet washers are supposed to be used initially to wet down and loosen
any surface dirt...not ingrained grime. THAT stuff should be removed
by the other 'attendants' with the sponges and soapy cleaner they use.
The spray off after washes off all the soapy stuff...
It is not to be used to try to 'etch' off any ingrained dirt that the soft
sponges and cleaning solution haven't managed to shift...ok.
Ingrained blemishes/marks/tar etc require removal by clay barring and
or by the use of a mild cutting compound akin to T-Cut.
So...from a general point of view...jet washes are a weekly rinse off,
whereas a proper clean you either do yourself, or...you entrust to a
reputable detailer once every 6 months or so, ok. The stuff they use
will really clean your car...and the waxes/polish they use should suffice
to keep your car clean and shiny for 6 months or so...with a wash down
in between to shift the surface dirt off the polished surface underneath.
As for the GRP panels....and what colour they are/were originally...
the base colouring of the material is a matt black of sorts. They are
then sprayed with an primer, undercoat, topcoat and finally sealed
with a coat of lacquer....just like all the other cars on the road.