Good question. So I asked the handsome and knowledgable Zman this, since he worked in the dairy business for many years. I thought the answer too was egg yolks……..WRONG! The big manufacturers all use powdered egg. Apparently there could be a couple of varying factors, if real liquid vanilla was used (opposed to powdered)this could change the color, but the big reason is COLORING. MikeSh was right. Another interesting fact about ice cream is that it is injected with air in the freezer. This is called "overrun" and is done so the ice cream will not be so dense and also protects against ice crystals.
There’s your Ice Cream 101 lesson for today. [;)]