It is unlawful to serve yellow-colored margarine without clear signage.

The Law Explained

Like many dairy-heavy states, South Dakota fiercely protected its butter industry from the rise of cheaper margarine. Old statutes mandated that restaurants serving margarine had to display a large sign notifying patrons, or else dye the margarine an unappetizing color. This was meant to stop sneaky diners from passing off the fake stuff as real cow's butter.