The beautiful colours that you can see on a soap bubble are the result of the interference of visible light waves off the front and back surfaces of the soap films membrane. The illustration below shows incident light waves striking the film with reflections from the top and bottom surfaces. These reflected light waves interfere with one another to suppress some colours and enhance others. The colours produce depend on the thickness of the film at that point. The thickness of the film changes continually due to laminar and turbulent currents of water gushing around within the lipid bilayer interior, from air currents brushing over the surface and due to shrinkage of the film due to draining.