Noticed a few brand new white cars with coded sills etc, anyone know if this is done at the factory and these pre-painted parts can be ordered (guessing not!)

Ahh, you mean the ice cream van edition??

The sills are only done once they get to the dealer, and mostly farm them out to the local body shop.
Some colours can carry it off, but IMHO White isn't one of them'
Cheers
Dave MY10 TDV6 SE (debadged ), Santorini Black, Flappy paddles, Privacy Glass, 20" Stormers, Mudflaps!

Gone: a comprehensive list of imprezas and a Merc ML AMG

Do you mean the new current reg models, you can spec colour keyed trim from the factory now?  ON THE WAY: BMW F21 M140i
MERCEDES GL350 - Metallic Navy Blue w/Grey interior

GOING: BMW F31 335D MSport+ xDrive Touring
GONE: Land Rover Discovery 4 HSE - Stornaway Grey w/Black Interior (wish we'd kept it )
GONE: BMW F10 520D MSport - Carbon Black
GONE:MY12 RRS SDV6 HSE Sumatra/Ivory/Grand Black Privacy glass

Bc is correct, mine was done at the factory, but mine is part of the Autobiography kit. And Codfather is also correct, some dealers get their own stock colour coded, siberian fox's car was one of them but had no end of trouble with panels coming loose paint peeling and way off colour match But that was down to the bodyshop not knowing what they were doing and foxy's colour was a brand new colour. Unless you know a very good bodyshop i'd opt for factory colour coded everytime but that means ordering a new vehicle