"Oleomargarine" and "margarine" are the same thing -- "oleo" as a regional dialect word turns up in a lot of places. My grandmother always called it "oleo" and my mother still does. The ban on dyed margarine was common in states with a strong dairy industry and lasted in some areas into the sixties. Nucoa brand margarine, put out by the Hellmans-Best Foods people, used to advertise that you should only use the dye pellet for "table use," and leave it white if you were just going to use it for cooking. If you've ever used Crisco shortening in stick form, that's exactly what uncolored oleo looked like.