When a beam of light travels in reverse, it does not undergo any changes in color or wavelength. The color or wavelength of light is determined by its frequency, and that remains constant regardless of the direction of travel.
Light consists of electromagnetic waves, and its color is determined by the frequency of these waves. Higher frequencies correspond to shorter wavelengths, which are associated with colors like blue and violet, while lower frequencies correspond to longer wavelengths, associated with colors like red and orange.
When light travels through a medium, it can interact with the medium, causing effects such as refraction, reflection, or absorption. However, these interactions do not alter the inherent color or wavelength of the light itself.
Therefore, if you were to reverse the direction of a beam of light without any interactions or changes to the medium it is traveling through, its color and wavelength would remain the same. The only change would be the direction of travel.