luminous, clarity, white, hoary
顥 centers on bright, clear light: luminous, white, or hoary. The meanings all describe something shining or pale with clarity.
顥 combines 景 (bright scene, sunlight) with 頁 (head), suggesting a bright or luminous appearance, especially of the head or face. The exact historical development is uncertain, but the component combination fits the meaning of whiteness or clarity.
The left side 景 shows a bright sun over a city, and the right side 頁 is a head. Imagine a head glowing with bright, white light, like a luminous halo.
For コウ, picture a bright, luminous coat glowing on a figure: coat -> コウ, and the white light makes everything clear.