Visible light is a portion of the electromagnetic spectrum that humans can see. When all the visible wavelengths are combined, the color of light is white. Shorter wavelengths produce violet colors and longer wavelengths produce red. As lightning passes through the atmosphere, air molecules will scatter the wavelengths of visible light. Shorter wavelengths scatter more than longer wavelengths. As light travels through more air, the shorter wavelengths are depleted until light will appear reddish. So, the more air between you and the light source, the redder an object appears.
Lightning flashes can reach temperatures of 30,000 K. At this temperature objects emit a brilliant white light. Observers close to a lightning strike or in an area free of pollutants and dust will may observe white lightning. The farther one is from the lightning strike, the amount of pollutants or particles in the air, types of atmospheric gases, and moisture can cause lightning to appear blue, purple, yellow, orange, or red.
Photographs of lightning can be affected by the type of film, camera, exposure, and white exposure used and may not be representative of the atmospheric conditions when the photograph was taken.