Nice comparison shot Shaun, I love this sort of thing! It speaks quite strongly to some types of collector, me included - if something is almost the same as something else, but just not quite identical, then it's the Pokémon effect - gotta catch 'em all!

Certainly for the Monacos and the contemporary Carreras, Heuer (or their dial supplier(s)) seem to have played around with the blue paints quite a bit, trying to find the ideal one. It's hard to tell with the passing of so much time, and lots of other variables like exposure to sun, but it seems to me that at different times some dials were prone to fading to violet, others to different shades of blue. This continues even through the introduction of Cal 15 watches. As I say, hard to be sure with so many environment variables to take into account, but it definitely seems to me there was a fair degree of variation in paint from new over time with both series of watches

I always think it's worth linking one of your earlier shots when discussion turns to this, so here it is again for posterity!