Soap bubble colors come from thin-film interference: light partially reflects off the film's outer surface and partially off its inner surface, and the two reflected waves recombine, reinforcing certain wavelengths and cancelling others depending on the film's thickness and the viewing angle. The film itself constantly wobbles because surface tension pulls it toward a minimal-energy shape while gravity drains liquid downward and stray air currents buffet it, all of which continuously change the local thickness. This is the same underlying physics as the rainbow sheen on an oil slick on wet pavement or the structural (non-pigment) color in butterfly wings and peacock feathers — color from interference of light waves rather than from dyes. As a film thins toward the point of popping, the color bands sweep through the visible spectrum and eventually fade to a dark "black film" patch just before rupture.

• Film thickness ranges from a few micrometers (thick, freshly formed) down to tens of nanometers just before popping.
• Soap solution surface tension is roughly 25–35 mN/m, much lower than pure water's ~72 mN/m, thanks to surfactant molecules.
• Gravity drainage pulls liquid downward over time, thinning the film at the top and shifting/compressing its color bands.
• Color at a given point follows Newton's thin-film interference formula, which relates hue directly to local thickness and viewing angle.
• A typical bubble survives anywhere from a few seconds to a couple of minutes before evaporation or drainage causes it to rupture.
• Near-total destructive interference produces the dark "black film" region often seen right before a bubble bursts.