Some of the light that impinges on the surface are reflected and the rest are transmitted to a different medium
At the surface of the next medium also, some of the light are transmitted while the others are reflected and refracted through the first medium
The speed of light (and hence the wavelength and color) refracted through the thin film is changed as the distance the refracted light travels through the thin film is increased as we move away from the point directly in the front view to some distance as the reflected light path from those distance to the eye is increased due to their inclination giving them a different wavelength which are all equal at a radial distance from the eye hence forming a circular fringes.
