Ionochromism is the name applied to the phenomenon of a colour change associated with the interaction of a compound or material with an ionic species. The organic structures that undergo the colour change on interaction with the ions are called ionochromes or ionophores. The colour change can be from colourless to coloured or vice versa and is usually reversible. Applications of these chromisms include reversible indicators in analytical chemistry and, more recently, colour-change cocktails.