Watch this bubble as it dissolves into drops. If you notice, the thinning portion loses it colors just before it bursts. Here's why time, and decay, sap bubbles of their colors.
These amazing photos of a breaking bubble show us the way color swirls on the bubble's surface. Experienced bubblers know that colors change on a bubble over time. Just before popping, the colors vanish altogether. The bubble turns to colorless light and darkness before it finally breaks up into drops.
Colors swirl on bubbles due to interference between two waves of light. When light hits the outside surface of a bubble, some of it reflects back towards the viewer. But there's another surface to a bubble - the inner one. Some light will also reflect back from this inner surface. These two waves of light will be slightly out of sync, and will interfere with each other. If a peak meets a trough, the two will cancel out. If a two peaks meet, they'll combine. The overall effect of this interference is one aggregate wave with a new frequency - which the person observing will see as a color.
When the bubble is thick, the waves from the outer and inner surface reflect toward the viewer from points that are - relatively - far apart from each other and so the waves interfere in a certain way. When parts of the bubble thin, the outer and inner wave reflect from surfaces that are closer to each other, and the interference pattern changes. The swirling colors we see are actually the swirls of different thicknesses of the liquid forming the bubble. As liquid evaporates from the bubble's surface, the bubble thins enough that the two waves are so close together that they don't interfere with each other much, and the light reflected from the bubble looks colorless, like the light around us.
Via Brocken Inaglory