marsh, pool, harmonious
雝 centers on a calm, enclosed body of water: a marsh or pool. The harmonious sense likely extends from the idea of still, balanced water.
雝 combines 邕 (a marsh or pool) with 隹 (a bird), suggesting a bird by a marsh. The harmonious meaning may derive from the calm scene.
The left side 邕 looks like a contained body of water, and the right side 隹 is a bird. Picture a bird standing peacefully by a marsh, creating a harmonious scene.
For ヨウ, imagine a yellow (イエロー) bird by the marsh: yellow -> ヨウ, and the bird's presence makes the scene harmonious.