Loved the small book "Soap-Bubbles and the Forces Which Mould Them" [1], [2], [3] by C. V. Boys.

He talks about the colors of soap bubbles (among other things). After reading it I watched a large bubble-sheet exhibit at the Exploratorium in San Francisco with fascination—noting how the colors were different at the top of the film, (where it is thinner) compared with the lower part of the film (where it is thicker).

As the bubble begins to evaporate and get thinner, it eventually becomes colorless (black, I suppose) just before popping.

Aside from the section on color, the whole book is a beautiful example of reasoning, the scientific method, etc. (as though presented to Physics students—but it is nonetheless easy for the layman to follow along).

[1] https://archive.org/details/soapbubblestheir0000cvbo/

[2] https://archive.org/details/SoapBubbles-English-C.V.Boys/

[3] https://www.gutenberg.org/ebooks/33370