This is probably due to the large amount of black charcoal that is needed to achieve a really dark colour. Then the coal has to be finely pulverised to finally turn white into a rich black. It's quite understandable that this can easily add up to 100, 200 or 300 francs. 🤷
These price differences in colours are undoubtedly a strange drive of capitalism. It comes from the car industry, when people started to declare a model new just because it was suddenly blue instead of green. As a customer, you should probably just go for the cheaper colour. Especially with a smartphone, it doesn't really matter whether it's green, white or pink. It really doesn't.

In fact, the difference lies in the supplier. We can buy the white version at much more favourable conditions than the black version here.
But the problem is on the market in general. With most suppliers, the white model costs less.