Cause for yellow color of butter

[Guest guest]

I recently spoke with a farmer from whom I buy goat's milk, and he said

that butter is white by nature, and yellow color comes from dyes people

add to it. Can anyone point me to a reliable source of info that proves

otherwise? Could he be right, but if it's butter made from a goat's

milk? I have such butter, and it's quite white. Maybe only butter made

from cow's milk can be yellow?

Thanks

Roman