Questions
 
Why do bubbles have color?

Rainbow
Similar to the way we perceive the colors in a rainbow or an oil slick, we see the colors in a bubble through the reflection and the refraction of light waves off the inner and outer surfaces of the bubble wall. You can't color a bubble since its wall is only a few millionths of an inch thick. A bubble reflects color from its surroundings.
Bubble Animation
Table Of Contents
Lots of color.
The bubble to the right is full of color because light
waves reflected off its thick walls reinforce one another.		 Colorful bubble.
When a light wave hits the surface of a bubble, part of the light is reflected back to a viewer's eye from the outer surface and part of the light is reflected from the inner surface which is a few millionths of an inch further.  As the two waves of light travel back, they interfere with one another causing what we know as color. When the waves reinforce each other, the color is more intense.  When the wave get close to canceling each other out, there is almost no color.   As a bubble wall gets thinner, either from a weak solution or because gravity has pulled its chemical content to the bottom, the distance between the inner surface and the outer surface of the bubble becomes less and less until the two reflected waves of light start to coincide and cancel each other out.  The result is that the bubble loses its color and can become nearly invisible.
Not much color.
The top of the frozen bubble to the right is extremely thin and appears to have become invisible as reflected light waves cancel each other out.		 Invisable bubble film.