Month and leap year display mechanism for timepieces

A month and leap year display mechanism (10) for a timepiece (1000), wherein said mechanism (10) comprises a leap year display integrated in a month display, said mechanism (10) comprising a movement (100) or being arranged to cooperate with a movement (100), which movement (100) is arranged to drive, via a control mechanism (3) comprised in said mechanism (10), a month display wheel set (2) rotating about an axis of rotation (D) and arranged underneath a cover plate or underneath a dial (1), and wherein a month window (1C) contained within an angular sector of 90° about said axis of rotation (D) is arranged to allow a user to see a quarter of said month display wheel set (2), the other three-quarters of said month display wheel set (2) being concealed from the user, and said control mechanism (3) being arranged to make said month display wheel set (2) complete one revolution in four years, and said month display wheel set (2) bearing, over an angular sector of 90°, at least one characteristic leap year marking, and either carrying indices, each arranged to indicate one month on a static month scale of said dial (1), or equidistant month markings of which one of these month markings is pointed to by a fixed mark of said dial (1), characterized in that said month window (1C) comprises an at least partially translucent crystal (70) bearing twelve translucent upper markings (71) of the months of the year and underneath which crystal (70) rotates said month display set (2) which bears four equidistant, coloured and/or reflective lower markings (72), each having the angular amplitude of one month marking and arranged to reveal the name of the current month by visual contrast with the upper markings (71) of the other months, wherein one of said lower markings (72) is a leap year lower marking (72A) and is different from the other lower markings (72) which are ordinary year lower markings (72B), and is arranged to produce, for the current month, a visual effect for the user which is different from the visual effects of the other months of the year.