All the eggs you find in France are brown. I've seen white eggs only once in the past 7½ years. They were being sold by a farmer at the market in Loches. I don't think he was selling anything but eggs, and he didn't have an awful lot of them. So I assume he kept chickens and the eggs were the product of his hens.
According to French Wikipedia, French chickens used to lay mainly white eggs. But French chickens were cross-bred with Asian breeds starting in about 1850, and now all the eggs are brown (called œufs rosés in French).
English Wikipedia says that, in general, "chicken breeds with white ear lobes lay white eggs, whereas chickens with red ear lobes lay brown eggs." Ear lobes? I guess I'm not very familiar with chicken anatomy, because I didn't know that chickens had visible external ears.
Different cultures have their preferences when it comes to eggshell color, but chicken eggs of one color are not inherently better that chicken eggs of other colors. In the U.S., at least where I lived, brown eggs used to be considered to be "better" than white eggs, but that is evidently not the case. One French friend told me she assumed that brown eggshells are not as fragile as white eggshells, and that's why egg merchants prefer them: less breakage. I don't know if that's true.
In France, the eggs are brown and they are often sold in cartons of 10, not 12. They are also sold by the half-dozen. The ones I bought in Loches a few days ago came in a pack of 24. Oh, and in the supermarkets they are not kept in refrigerated cases. They're just out on the shelves like the bags of flour and sugar.