My husband taught me today that butter is yellow because it contains Vitamin A. He heard this on a TV show and thought it was pretty interesting. I looked it up and he is right. The cows eat grass that contains beta carotene and precursers to Vitamin A and that comes out in the color of their butter. Grazing cows get more sun and produce more Vitamin A. Herds of cows that are raised in shade do not have this exposure to the sun and Vitamin A is added at the processing plant. More info can be found here.
There you go...a bit of useless, yet interesting information!