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Old style geometric optics describes their reflections but we must use wave optics to explain their colors. Surface tension forces battle to keep bubbles envelopes spherical. To understand why they exist at all needs some attention as to why certain molecules stick together while rejecting others.
Reflections: Look carefully at the reflections. There are two images. The upper one is upright and the lower inverted. The bottom picture shows the upright image most clearly. The upright image is from the bubble's front surface that acts as a convex mirror. The inverted image is from the bubble's rear surface acting as a large concave mirror.
Interference colors: The vivid iridescent and ever changing colors are from thin-film interference seen because soap bubble films are a mere few wavelengths of light across.
Imagine skylight reaching the outer bubble surface. Some is directly reflected. Some enters the film and part of that is then reflected back by the inner film surface to leave the bubble in the same direction as the directly reflected waves.
The two outgoing wave trains overlap and interfere. In some directions - and for some colors - the wave crests correspond. That particular direction and color will be bright. In other directions or colors the two outgoing waves might be out of phase and cancel. The rear bubble surface independently contributes a second set of interferences.