From records these were reasonable pullers (for the day) although quite slow with a top speed ~30km/h.
In terms of colours, they were obviously black but for some reason I'm thinking that they has a gold (or gold coloured) trim on the side of the tender & cab, and polished straps on the boiler (this comes from my father modelling one when I was younger).
From what I've seen, the cab and tender would be black with gold lining, and the boiler bands would definitely be brass, judging by the photos. Um. The main question left is whether the boiler would still be Russian Iron or black. I'm assuming that the engines in your photos would likely have brass cylinder heads.
http://www.trainweb.org/nzsteam/images/t_class.jpg is the engine I've modelled, and I suspect it'd more likely have black cylinder heads.
I'm glad those photos have the engines' numbers on them, that means I can model each one.
Um, the engine's top speed was well over 18mph, however that was the speed limit of the trains they usually pulled, especially on the North Island. Some did pull the occasional passenger service, however, and could reach a pretty good clip, although I could never find out how quick.
Looking at the photos you linked, it's funny. The second must be fairly early, as it seems only to have had it's boiler replaced, safety chains added and stack shortened.
Anyway, something to think about.
