Reversibly thermochromic composition and reversibly thermochromic microcapsule pigment encapsulating the same

A reversibly thermochromic composition comprising:

• (a) a pyridine derivative represented by the following formula (A), as an electron-donating color-developing organic compound;
• (b) an electron-accepting compound;
• and
• (c) a reaction medium which reversibly induces an electron transfer reaction between the component (a) and the component (b) in a specific temperature range:
• (wherein,
• each RA1 is independently hydrogen, a halogen group, or a linear or branched alkoxy group having 1 to 6 carbon atoms, provided that at least one of RA1 is an alkoxy group,
• each mA is independently an integer of 1 to 3,
• lA is an integer of 1 or 2, and
• X is hydrogen or a group represented by the following formula:
• wherein, each RA2 is independently hydrogen, a linear or branched alkyl group having 1 to 6 carbon atoms, or a linear or branched alkoxy group having 1 to 6 carbon atoms, and
• each nA is independently an integer of 1 to 3,
• provided that two X never simultaneously form hydrogen and never simultaneously form a phenyl group).