The wonderful thing about contradicting what one has said previously is that it implies that one is wiser today than one was yesterday!
And thus, I am about to offer some clarification on my previous post. I have always maintained that black Constellation dials with white lettering are not to factory specifications. In correspondence with Omega some time ago, I was informed that Omega did not produce black dials with white script in respect to 1950s and 60s Constellations. However I had cause for pause when Per Baun Christensen sent me the pictures featured in the post below. The original magnified pictures confirmed, in my opinion, that the dial was genuine.
What I did not consider, however, was the possibility of the white-looking script being in fact silver lettering that had degraded over time. Dial paint and lettering does deteriorate when in contact with either moisture or the sun. Top lacquers crack and degrade as a natural course, and unless a dial spends its life in a safe there's little guarantee of it remaining in its pristine state.
Tim Mackrain, offered the observation that the white script featured in my previous post may, in fact, be silver lettering that had lost most of its 'silvery-ness'. He examined in detail the dial above and detected definite traces of silver in the script. The dial is clearly a genuine dial because the reverse of the dial (pictured) shows no tell-tale glue or re-soldering and has the original machine marks that smoothed off any minute metal particles attached to the rivets on the applied markers and Omega logo.
Further checks are being made on Per Baum's dial and I suspect that under magnification the script will show some traces of silver.
So, the standard appears to be: 1. No dial with white script is correct, 2. black dials with gold markers and hands should have gold lettering, and 3. black dials with rhodium plated markers and hands should have silver lettering, sometimes degraded to the point that it looks white.
Because of the preponderance of black dials on Omega Constellations and indeed many other models, particular care needs to be taken to ensure that any degraded black dials with what appears to be white lettering have some trace of silver.
Black dials are popular on Omegas, and some online and bricks and mortar dealers are refinishing in black because the watches sell for higher prices. It may pay to remember that black was rare on most Omega models of the 50s and 60s and that most examples available are refinished previously ivory or silver dials.