The phrase describes a specific color variation within the popular Koi Tang species, Zebrasoma flavescens. This variation manifests as a blue coloration primarily on the face of the fish, differentiating it from the typical yellow coloration found in the standard Koi Tang. This specific color pattern is highly sought after within the aquarium hobby.
The occurrence of this unique blue facial marking enhances the aesthetic appeal of the fish, increasing its value and desirability among saltwater aquarium enthusiasts. Its relative rarity compared to the standard yellow morph contributes to its heightened significance in the aquarium trade. Historical context is limited, as the observed variation is a naturally occurring phenomenon, not selectively bred or genetically engineered.
