an orange color, hide, conceal
韞 centers on the idea of keeping something out of sight: hiding, concealing, or wrapping something away. The meaning "an orange color" is a separate, rare sense that does not clearly connect to concealment.
韞 combines 韋 (leather, tanned hide) with 昷, which likely contributes the sound. The idea of wrapping or concealing may relate to leather as a covering material, but the exact historical development is uncertain.
The left side 韋 suggests leather or a covering, and the right side 昷 looks like a container with something inside. Picture wrapping an object in leather and placing it in a covered container to hide it away.
For オン, imagine turning 'on' a hidden switch inside a leather pouch: on -> オン, and the switch is concealed within.