Yellow used to be illegal

Delrich Margarine advertisement, The American Weekly (Week of October 10, 1948)

Margarine was invented in the 1869 as a lower-cost replacement for butter. Since that time dairy producers have rightfully seen margarine as a serious threat to butter sales.

In the United States one response was to pressure lawmakers to prohibit margarine makers from producing a product that looked like butter. Margarine was required to be white, although manufacturers could include yellow colouring with the margarine as long as the consumer was responsible for mixing in the dye. In January 1948, William Dennison filled a US patent for "Oleomargarine package and method of making". The plastic package included a "color berry" with the required yellow colouring.  This eliminated the need to mix the margarine and dye in a bowl.

The "color berry" is long gone, but it was not until 2008 that margarine producers in Quebec were permitted to sell their product in "butter yellow".