Oleo, commonly known as margarine, has a long and controversial history in Wisconsin. It only became legal to buy yellow oleo in the dairy state on July 1, 1967, after years of contention.

The controversy started in 1895, when the state Legislature first passed a law forbidding the manufacture or sale of butter-colored oleo. Dairy advocates didn't want oleo to compete with butter by looking more like it, but it remained legal to sell the naturally pale white oleo. 

In 1931, more than 5,000 farmers marched to the Capitol to seek to block an underground system of bringing yellow oleo into the state. The Legislature responded with a tax on the fake butter, which was much less expensive than the real thing. After World War II, housewives crossed state lines to bring in the substance. The struggle over oleo reached a climax when one of its loudest foes — the late Sen. Gordon Roseleip, R-Darlington — agreed to take a blindfolded taste test of butter and oleomargarine. He failed the test, and it was later revealed that his wife had been feeding him colored oleo while telling him it was butter. Here's a look back at the issue over the years.