A trade-name for a blue which retains its color under artificial light.(noun)
The Century Dictionary (Public Domain)
Use "night-blue" in a sentence
"The clear water got deeper, then shallow again, as they raced over iridescent carpets of night-blue mussels."
"Resplendent in her glittering night-blue dragon-scale armor, Kitiara stepped haughtily to one side as Tanis walked through the ornate doorway into the Hall of Audience."
"His hand shaking, he reached for the next night-blue bound book in the huge pile he had amassed at his side."