1. The colours seen in a soap bubble arise from interference of light reflecting off the front and back surfaces of the thin soap film. Depending on the thickness of the film of soap, different colours interfere constructively and destructively.
2. Dichroic cubes have several surfaces that transmit light of a certain waveband and reflect its complement. They have dielectric coatings that result in a steep transition between the region of transmission and reflection, which is sensitive to the angle of view - hence these clear cubes appear multicolour viewed with a white light source
3. A CD is made up of thousands of pits arranged in the form of spiral tracks. When visible light is incident on the pits, each pit diffracts light in all directions. They act as a diffraction grating separating a light into its constituents forming rainbow colours. The colours that overlap are seen brighter than the colours that cancel each other.