“Since margarine intrinsically appears white or almost white, by preventing the addition of artificial coloring agents, legislators found they could protect the dairy industries by discouraging the consumption of margarine based on visual appeal. If margarine were colored the same as butter, consumers would see it as being virtually the same thing as butter, and as a quasi-natural product. Bans on adding color became commonplace (...)” https://en.wikipedia.org/wiki/Margarine#Legal_issues