Shaun, I've seen silver text Datos with white registers, silver registers and an intermediate version that is silver but not as strongly metallic as your example. If I had to pick one from those as standard, it would probably be that last one - the very silvery version like yours does seem to be more unusual.

There's a guy at the Munich watch fair who more or less specialises in the Heuer triple calendars and it's really interesting to see their (slow) evolution over time. Attaching the Carrera name was a nascent attempt at marketing from Heuer, given the line remains more or less unbroken from the triple cals of the 40s and 50s - the marketing even makes it through to some of the brochures, where it's given as "Heuer's executive watch".