I find it fascinating how this glint from the sun appears multiple times at the top edge. The gaps get smaller towards the edge. There's probably some beautiful math formula for this involving the golden ratio.
I'm no lightologist - But I think the two different colors and inversion is seeing the reflection on the outside of the bubble on one hemisphere, and THROUGH the bubble to the inside surface of the opposite side.
* 2 cups Washing Up Liquid (dish soap in the USA my sister-in-law recommends Dawn Dish Soap)
* 1 tablespoon of glycerin
* Few Drops of vegetable oil
* 1 cup Warm Water