Heat the oil in a large skillet over medium heat. Add the purple and yellow onions. Sauté 5 minutes or until the onions begin to soften. Add the green onions, cover and cook 8 minutes longer.
Increase heat to high and add the vinegar. Cook, stirring occasionally until liquid is reduced by half, about 8 minutes. Add the sugar, salt and pepper. Reduce the heat to low and continue cooking until the liquid is almost absorbed and the marmalade is thick, about 10 minutes. Serve warm
Recipe by The Tennessee Magazine at https://www.tnmagazine.org/flavor-from-the-underground/