These are caused by reflection of light from the two sides of the thin film of water forming the bubble.
这些是由形成气泡的水薄膜两侧的光反射引起的。
英语百科
Film-forming agent
（重定向自Film forming）
Film-forming agents are a group of chemicals that leave a pliable, cohesive, and continuous covering over the hair or skin when applied to their surface. This film has strong hydrophilic properties and leaves a smooth feel on skin.
Film-forming agents include polyvinylpyrrolidone (PVP), acrylates, acrylamides, and copolymers.