It's a good question Ron!

First off, those watches in the catalogues are 3647s, aka Carrera 45s, so have the Valjoux 92 movement rather than a 7730. And that's quite important overall for our contrasting dial story.

Winding back to 1964, when the Carrera was introduced, the overriding mantra in its design was simplicity. The contemporary Autavias had a more elaborate dial with arabic numerals and dauphine hands (though these were being phased out by the Carrera launch) and, yes, contrasting dials. Now, it's a question for Jack Heuer whether the Carrera had matching dial and registers for ultimate readability, but it seems a deliberate choice compared to the Autavia. It's also debatable whether the eye is drawn more to contrast registers or if they are a distraction - certainly by the second generation of Carrera, at least 4 out of 5 Carreras did have contrast registers, so perhaps they'd changed their minds or maybe style was becoming more of a consideration with the advent of the 70s.

Now, moving forward to somewhere around 1966 and the introduction of the 45 Dato, we see Heuer still sticking with its monochrome dials for the Carrera. For the first execution, at least. Then, all of a sudden, the second execution comes out and the black-dialled version (and only the black-dialled version, the silver one has a silver register) has a white register:

So that sets a precedent, but Heuer doesn't seem to do anything with it for another couple of years.

Then, somewhere around 1969, the Carrera goes a pretty comprehensive revision. The Carrera 45 is dropped and replaced with the 30, dial markers and hands are changed to versions with added detailing. And this is also the point at which we start to see the contrast dials appearing, on both the Carrera 12 and the 12 Dato:

It's possible that the Datos had started to have contrast dials a little earlier in fact, but the very earliest ones didn't. I think it's fairly conclusive that the first Carreras with contrast dials were Datos, whether it be 12s or 45s.

Every now and again, we do see a Carrera 12 with contrast registers in first execution.

Some of these looks like redials, but this one looks genuine - it may well be a prototype for what Heuer were planning to introduce more widely in the second execution. Certainly, the vast majority of contrast dials we see are second execution. Interestingly, though, they don't appear in catalogues - only open to special order perhaps? I'd wager not, since there seems to be enough about that they're not ultra rare.

You'll note that I've been talking about 12s mainly, not the 45s and 30s (the two register variants) you asked about. And that's because we hardly ever see them with contrast registers. We DO, however, see them in a catalogue, unlike the 12s:

Ignore the first two, those are economy models, it's the third one we're after, the 7753 T. So I think we're getting close to an answer for our question. Two dial first generation Carreras only seemed to have contrast dials with this model and its close sister the 7753 D and then only for a limited time - both were introduced with single coloured dials and had a contrast configuration only at the end of their lives, for under a year. And selling against the brand spanking new Chronomatic-powered 1153.

So the simple answer seems to be we see so few contrast register 2 dial first generation Carreras because very few made it out of the door. We did see one on here a while back, from Stepan, but I can't remember seeing any in the metal. Would be interested in hearing from anyone who has!