Minister, waht happend was that in 1955, when the earliest laminates, Park Royals, and of course the "A" class locos arrived, they decided that they might look wll in silver and it would save paint and time. As photos show, they couldn't have been more wrong - anything left unpainted deteriorated almost as soon as it entered traffic. How they could expect loco bogies to remain silver is a mystery! Subsequent deliveries of the three G601s and the B1013 were also initially unpainted.
Interesting livery detail: locos had a snail and number in "eau-de-nil" but at least some carriages and tin vans had numerals in red, possibly all at first. No silver rolling stock ever carried "snails" - just the numeral.
By the early 60s, silver was dying out. It is likely that some stock went straight to black'n'tan.
In all cases, at first repaint, they received the post-55 lighter green.