beautiful (as a jewel)
瑤 centers on the radiant beauty of a precious jewel, describing something as exquisite and gem-like.
瑤 combines 王 (jade/gem) with 䍃, which likely contributes the sound and may have originally depicted a kiln or vessel, but the exact historical development is uncertain.
The left side 王 (jade) signals a precious stone, and the right side 䍃 looks like a decorated container. Imagine a jewel so beautiful it is kept in a special ornate vessel.
For ヨウ, picture a beautiful jewel glowing with a soft yo-yo light: yo -> ヨウ, and the gem's radiance swings gently like a yo-yo.