If I understand correctly......Bindi is kind of something you wear in the forehead, just like we use lipstick/gloss for our lips...@ B......maybe I'm missing anything...don't know the relation between those 2?
Modern bindis are like a velvety sticker and you're correct, it's an accessory. But, for some it holds religious significance...so a lot of married women wear red bindis. So, in the olden days when widows were treated like crap...they were forced by traditions to stop dressing up to look pretty & were told to wear white only. So, they would also stop wearing bindis, bangles, etc.