Question

Due to effect of interference floating oil layer in water is visible colour

Answer 1

The brightest colours whose interface is constructively seen in float an oil slick on water or with a soap bubble which is caused by the interface. As we observed the interface effects most prominent lights which they interact when something is similar to the wavelength.

The interface between the light is reflated from various face and also led the film effects with a thin film interface. A thin film has thickness t with the smallest wavelength of light λ.

Since the colour is indirectly associated with λ and since all interference is in some way dependent on the ratio of λ to the size of the object concerned