"Pixel crack" is a slang term used to refer to brightly-hued artwork in games, especially massively multiplayer online games or simply in reference to the games themselves. The term is a reference to the addictive qualities of cocaine.
Items that are given such a hue by developers are sometimes created for the sole purpose of collection by players, and are often sought after for their rarity or simply for their ability to draw the eye of other players. Amassing large quantities of such items is a hobby of many in online games.
Pixel crack may also refer to entire games.