glistening plumage, reflection of the sun on water
翯 centers on a bright, glossy sheen: the glistening of feathers or the shimmering reflection of sunlight on water. Both meanings share the idea of a smooth, luminous surface catching light.
翯 combines 羽 (feathers) with 高 (tall, high), likely suggesting the bright, glossy appearance of feathers raised or catching light. The exact historical development is uncertain.
Feathers (羽) raised high (高) catch the sun and glisten. Picture a bird with plumage held tall, each feather shining like sunlight on water.
For コク, imagine a glossy-feathered bird perched on a tall rock: rock -> コク, and the bird's plumage glistens in the sun.