[beermantm]

Margarine was originally manufactured to fatten turkeys. When it killed
the turkeys, the people who had put all the money into the research
wanted a payback so they put their heads together to figure out what to
do with this product to get their money back. It was a white substance
with no food appeal so they added the yellow coloring and sold it to
people to use in place of butter. How do you like it? They have come out
with some clever new flavorings.

Urban Legends Reference Pages: The Butter Truth