dark purple (highest-ranking officials' color)
A rare historical term for a deep purple shade once reserved for the highest-ranking court officials in ancient Japan.
至極色 refers to a deep purple that, in ancient times, only the highest-ranking officials were permitted to wear.
Compound of 至極 (しごく, 'supreme, exceedingly') and 色 (いろ, 'color'), literally 'supreme color', reflecting its exclusive use by the highest-ranking officials.