A reversible thermochromic composition comprises (a) an electron-donating color-developing organic compound, (b) at least one electron-accepting compound selected from alkoxyphenols compounds of the formula
and (c) a compound serving as a reaction medium capable of causing a reversible electron-donating/accepting reaction attributable to components (a) and (b).
This composition has a reversible metachromatic function; in one aspect, it presents a color-developed state when heated from a color-extinguished state and presents the color-extinguished state when cooled from the color-developed state; in another aspect, it begins to develop color during the course of being cooled after having been heated, color development having been triggered by the temperature rise when being heated in a color-extinguished state, and returns to the color-extinguished state after presenting a maximum developed-color density.