lets use a VP SS as an example here
OK the offical Holden colour will be called something like archetype grey, the car dealer may advertise the car as Grey and when you go to motor reg the car will be registered as Black.
Holden only do one shade of silver normally so if you want a 08 made Nickle SV6 a 08 made Silver is the same colour. There is also a colour code, so if your deadset of the colour get the code from Holden and check that the car your buying has the same paint code. Code should be somewhere in the engine bay along with the trim code, paint, trans, enigine etc on a Alloy ID plate