the countenance changing
艴 centers on a visible shift in facial expression, specifically the countenance changing, often due to emotion.
艴 combines 弗 (a phonetic element) with 色 (color, countenance), suggesting a change in facial expression. The exact historical development is uncertain.
The left side 弗 looks like a bow being drawn, and the right side 色 means color or countenance. Imagine pulling a bowstring that suddenly changes the color of your face, as your countenance shifts.
For ホツ, imagine a hot flash of emotion that makes your countenance change: hot -> ホツ, and your face flushes.