eighth month of the lunar calendar
Archaic term for the eighth month of the old lunar calendar, equivalent to modern September–October. Cross-referenced with 葉月 (はづき), a more common archaic name for the same month.
See also: 葉月
其色月 is an old name for the eighth month of the lunar calendar.
The exact derivation is uncertain; the kanji 其色月 literally suggest 'that-color moon', possibly referring to the autumn moon, but this is speculative.