Basically this occurs by a phenomenon of destructive and constructive interference on light. When the movie is too thin it ends up exposed to an intense white light that was divided into a reflection both at the top and bottom of the movie.
Those rays can now interfere with each other, and this is what generates the colors. For the human eye, said position of the film generates the interfering waves that were generated by constructive interference. Said wavelengths in the form of colors will be present in the interference strip. Therefore the colors for which the destructive interference condition is met will end absent. Only those of constructive interference will be present.
