The color depends on the thickness. It is based on which wavelengths multiple it is, so will cycle through the wavelengths repeatedly, i.e. through the colors, as the bubble gets thinner.
The liquid is probably flowing out of the bubble onto the ground in a slow controlled way, until the bubble gets too thin and pops.

You can also use color rings to tell how gravity and wind are pulling on bubbles, and adding fluid to them should also cycle through the colors. When you attach them to the dispense you can see liquid flow into the bubble.