The Von Restorff Effect

The tendency to recall an item that "stands out like a purple cow" more easily than other items in a group.

A phenomenon of memory in which radically different things are more easily recalled than ordinary things. Memorizing isn't simply a matter of repetition. Attention plays a role in organizing material in ways that influence its later recall. For example, in any given number of items to be learned, an item that is different from the rest in size, colour, or other basic characteristics will be more readily recalled, such as a word printed in differently coloured ink or hi-lighted on a grocery list. 

This bias is named after the German psychologist Hedwig von Restorff (1906–1962) who first reported it in 1933. Also known as The Isolation Effect.