Genealogy make it very obvious. If your forefathers came from France, and your culture and ethnicity is consistent with what is French, then you are French. If your grandfather came from Senegal, what does it matter where you were born? French water is great, but it doesn't change your DNA.
Is there any native French left in Paris?
Define native, most of, if not all of the colored in France today, are born in France.
Do they have to produce an ancestor passport at least 10-20 French generations back?
Genealogy make it very obvious. If your forefathers came from France, and your culture and ethnicity is consistent with what is French, then you are French. If your grandfather came from Senegal, what does it matter where you were born? French water is great, but it doesn't change your DNA.
Plenty. But there is an unfortunate amount of 'diversity', and the city has deteriorated massively since I first visited.
If you mean actual White French? Hardly any.
They are all some mixed breed concoction of Arab, African, and surprisingly quite a few Asians... but mostly the first two.