noun, noun which may take the genitive case particle 'no'
steel blue
A dark, slightly grayish blue color reminiscent of steel. Used as both a noun and a no-adjective.
He was wearing a steel blue suit.
The sky was dyed steel blue.
Compound of 鋼 (はがね, 'steel') and 色 (いろ, 'color'). The exact historical derivation is uncertain, but the word straightforwardly describes the color of steel.