noun, noun which may take the genitive case particle 'no'
A vivid deep blue color, originally made from ground lapis lazuli. Used as a noun or with の to describe something as ultramarine.
彼女は群青色のドレスを着ていた。
She was wearing an ultramarine dress.
空が群青色に染まっていく。
The sky is turning ultramarine.
青色 is a general term for blue, whereas 群青色 refers specifically to the ultramarine shade.
群青 (ぐんじょう, 'ultramarine') + 色 (いろ, 'color'). 群青 originally referred to the pigment made from lapis lazuli, which was imported from distant lands (群れる, 'to gather', suggesting a gathering of many colors or a deep, rich hue).