Gather round, children, and hear a tale of baffling legislative stupidity that will anger up the blood! It seems that, in 1947, margarine was sold white, and had to be colored yellow by the end user. Why? Because the lawmakers at the time were dickheads, just like they are now. Dig it...
Note: Say what you want about Wikipedia, but the article there on margarine is clearly referenced. The external links and sources for the information are so thorough, all the facts look rock solid to me.
No sooner had margarine been invented (1869) than dairy farmers threw a tantrum. (Just in case you've spent the last 140 years with your head in a bucket of cement, margarine tastes a lot like butter with much less fat, making it more desirable than butter to lots of people).
In 1877, the United States began passing laws to make it hard for margarine to have a fair chance in the marketplace. Everything from extra taxes to expensive manufacturing licenses were dreamed up to prevent the low-fat butter substitute from gaining traction.
Margarine is pretty much vegetable oils, salt, and skim milk. In it's original state it's white. In order to resemble butter, yellow coloring must be added, and this was the deterrent generally settled upon by legislators in countries around the world, terrified of the destructive power of margarine. It became illegal to sell yellow margarine, thanks to the efforts of the dairy industry's lobbyists. In New Hampshire, lawmakers even tried to force margarine manufacturers to color it pink, hoping to make the stuff too gross to eat.(My country, tiiis of theee....). So, one of the workarounds devised by margarine makers was to sell the white margarine to consumers and have them color it themselves at home
This special package from Delrich had a little pimple of dye on the wall of the bag. Burst the pimple by pinching it and the dye was released into the bag. Squish it up for a while and you had a bag of safe legal, yellow margarine, and nobody would go to jail.
Here's a link to a USA Today article about obsolete unenforced margarine laws that were still on the books as recently as 2008.
These retarded laws remind me of the panic over CD ripping, and before that, VHS decks, and before that, cassette recordings of vinyl albums. In time, the lobbyists are proven to be panicky spazzes and the world completely fails to come to an end just because consumers are able to put their albums on cassette or are given an alternative to butter.
It seems that, if any new technology is met with fierce legal opposition, it's probably a good idea that will generally help people.