This is called constructive interference. If one wave pushes up and the other pushes down, the two pushes cancel each other and the water doesn't move at all. When this happens, it's called destructive interference. Light waves, like water waves, can interfere with each other. When light waves reflecting from one layer of soap molecules meet up with light waves reflecting from the second layer of soap molecules, the two sets of waves interfere.
Some waves add together, making certain frequencies or colors of light brighter.
Other waves cancel each other, removing a frequency or color from the mixture. The colors that you see are what's left after the light waves interfere. They're called interference colors. Each color corresponds to a certain thickness of the soap film. By causing the liquid bubble film to flow and change in thickness, a puff of wind makes the bubble colors swirl and change.