Drop some water on your new cream-coloured blouse and you get a dark spot. Have you buffon standing near you spill his perrier on your navy blue blazer and the light liquid somehow manages to make the coat’s dark colour even darker. Why is this so?
Elementary physics, it turns out. You lose the true colour of the garment in three ways:
Firstly, even a thin coating of water will force light comming towards the garment to refract within the water film. The available light is thus dispersed.
Secondly, the reflection on the surface of the water causes incoherent light scattering.
And finally, a combination of the two points above ensures that the will be less light available on the surface of the jacket to reflect back to your eyes. Thus the spot will appear darker than the rest of the jacket taht doesn’t have to compete with water in order to reflect light.