It looks painted too me as well after focusing on the 4 and 5 o' clock markers. The black only shows on the top.
I looked at one of my Constellations with onyx and this is how it should look. You can see the black onyx is an actual bar slotted into the hour markers. The side is black as well.
I'm pretty sure the painted ones are how they were originally made. Not every dial has onyx inserts.
Personally, onyx inserts are a nice to have. They wouldn't be a deciding factor for me if everything else looks good (dial, lugs, case, crown, caseback, movement, crystal).
But watches are about the details. Once you see it, you can't unsee it. If it bothers you so much, just wait for the next one. Plenty out there.