There are many various descriptors for red, orange and yellow. In Italian an egg yolk is called "rosso" (red), whereas in Swedish it's called "gula" (yellow). As a side note, Orange (the fruit) is called "Apelsin" in Sweden - meaning "Apple from China", just as in Dutch. Red onions would nowadays be categorized as mostly purple, etc.
> In Italian an egg yolk is called "rosso" (red), whereas in Swedish it's called "gula" (yellow).
In this case, it's possible that the different conventions for what color to call an egg yolk originated from egg yolks that were different colors. Crack an egg in China and you'll get something that is obviously different -- and much redder -- than what you'd get from an egg in the US.
This freaked me out enough that I exclusively purchased high-end eggs from City Shop, which were a reassuring yellow.