High School Question about the color of a thin film

[Antoha1]

TL;DR

Color of thin film if monochromatic light is pointed against it

If monochromatic light is pointed directly at thin film, film's color can only vary in intensiveness of that particular color of light, because of interference. So, if light is pointed at it, so it is maximum or minimum or neither of interference. The color apeared can only be the color of light pointed (the same wavelenght). If we start changing angle of direction of light pointed to the film, the color of the film changes from no color (minimum of interference) to the color pointed (maximum of interference) with no any other colors (wavelenghts) of light apeared. asking if this is correct. The space is fully isolated from any other light sources.

 

[Ibix]

Yes, ideally the brightnness of the reflection will vary and that's all. In reality, all sources have some bandwidth (they are not perfectly monochromatic), so in an actual experiment there would be some variation in reflected spectrum.

 

[renormalize]

TL;DR: Color of thin film if monochromatic light is pointed against it

Yes, your reasoning is correct. Take a look at: https://www.soapbubble.dk/en/articles/thin-film-interference which shows a half soap-bubble illuminated by a monochromatic sodium-vapor lamp of wavelength $589\,\text{nm}$: