Pour your bubble mix onto a black plate (about 20ml each). Use a straw to blow as large a bubble as possible (blow long and slow).
Look at the colours. Hold a sheet of white paper behind the plate at an angle to see more colours.
Why are they there? Made by the layers of soap molecules - refer drawing of structure to explain. (Light is made of many colours - when white light bounces of the first layer and the second layer the colours interact with each other and some colours are taken away leaving the others - called interference). So see all the colours in white light.
The colours in oil or on a CD are formed in the same way. Rainbow colours and colours from a prism are also formed from the separation of white light into its component colours, but by a different mechanism (refraction).