I was going to say that it depends upon who's making it what it is that makes it yellow.
I suspect most Spanish folks use saffron. That's what they use at my favorite Spanish restaurant in New York, and what I use when I make it. But I suspect most Indian folks would use turmeric. and I suspect most boxed products are mainly annato.
Otherwise, it would depend upon what flavor you want in your rice which "yellower" you use.