How do the colorful rainbow colors get into the soap bubbles?

Quick answer:

The rainbow colors enter the soap bubble
because different colored
light waves are reflected and superimposed differently on the soap bubble surface.

Prof. Pusti explains

The soap bubble shimmers in all colors of the rainbow and shows all 7 components of the light visible to us: red, orange, yellow, green, blue, indigo and violet.

The individual colors of the light move in waves of different lengths.

The soap bubble layer is less than a thousandth of a millimeter thin and thus approximately as thick as the wavelengths of the light. When the light is reflected by the inner and outer layers of the bubble skin, the different light waves overlap.

Depending on the thickness of the soap film, individual colors of the light are erased or intensified during reflection. Depending on the thickness of the soap film, individual colors of the light are erased or intensified during reflection. The counter color of the hidden color becomes visible to the eye. If, for example, green is faded out by the reflection, the soap bubble shimmers red at this point.

This superposition of light rays caused by reflection is called the interference effect. With the help of this effect it is also possible to observe the thickness of the soap skin and its change:

If the soap bubble skin is relatively thick, only the longest light wave, red, is faded out and the soap bubble appears green. If the skin becomes thinner with time, the soap bubble shimmers blue until it finally appears almost black.

Since the liquid in the soap bubble is pulled downwards by gravity, the soap skin is thinner at the top than at the bottom. The constant change in the thickness of the soap skin due to gravity and evaporation is clearly visible in the iridescent play of colors of the soap skin.