Color of light is said to be due to the difference of wavelength. But it seems to be due to the difference of frequency. Because, when an observer moves relative to light source, color of light will vary. In this situation, wavelength of coming light cannot vary.

The same light rays (laser) are emitted into water and air. Frequency in both medias is the same, but wavelength is different. What is color of color films exposed in both medias ?
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