I know I’m coming into this late in the game…
The Sefer HaChinuch writes that, while according to Halacha Kiddushin can be performed with any marginally valuable item, the custom is to utilize a ring. The reason he gives is that it serves as a “constant reminder” to her status.
Joseph- a ring is far less obvious to others than a large necklace; obviously the reminder is intended for the woman herself. I’m pretty sure a woman is constantly aware that she is wearing a wig especially as they aren’t known to be particularly comfortable.
Is there any prettiness lacking in nice hats and fancy tichels?
So even according to R’ Ovadia Yosef a woman may look pretty. I think it’s obvious when a women is a tzanua and when a woman isn’t; and it isn’t related to what type of covering is on her head. An immodest woman can be wearing a black headscarf and she’ll still give off the wrong impression.