which colour of light is least scattered by the fog or smoke

Visible light is composed of seven colour having different wavelengths.The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light and are more effective in scattering light of shorter wavelengths like the blue end than light of longer wavelengths at the red end.The red light has a wavelength about 1.8 times greater than blue light.Thus, when sunlight passes through the atmosphere, the fine particles in air scatter the light of shorter wavelength more strongly than red(having more wavelength).The red is the colour which is least scattered by fog or smoke.Therefore, it can be seen at a distance thats why danger signal lights are red in colour.