Butter, like cheese and ice cream, enjoys an exception to the labeling rules for food additives. Its natural color varies from white to pale yellow depending on the diet and conditions of the dairy cows; food dye provides a more uniform look.

The loophole has its roots in the late-19^th century, when margarine began to emerge as a cheap substitute for natural butter. To make the new product more palatable, manufacturers added a yellow dye. The dairy farmers objected, and lobbied Congress to pass the Oleomargarine Act of 1886, which imposed a penalty tax on any margarine that was colored to look like butter. The law also gave the dairy farmers the explicit right to use their own color additives. Around the turn of the century, these discriminatory color laws were widespread: 32 states had banned yellow margarine; some had even forced manufacturers to dye their product an unappetizing pink. (In 1967, Wisconsin became the last state to repeal its anti-color law.)