Pickled onions are usually pickled in malt vinegar and the onions are about an inch in diameter. Silverskin onions are pickled in white vinegar, and are much smaller. Full sized onions, e.g. Spanish Onions, can be pickled if sliced first.
In Mexican cuisine, one preparation, cebollas curtidas, has sliced red onions pickled in a mixture of citrus juices and vinegar, which is served as a garnish or condiment. Sometimes cooked beets are added, producing a more strongly pink coloured dish.
Sliced pickled onions atop a sandwich
A dish of pickled silverskin onions
Dutch Amsterdamse uitjes (at left): small onions pickled with spices; the yellow colour is from either turmeric or saffron. Here served with ossenworst (smoked minced beef).