First, please do not try to view lightening bolts while standing outside. Be safe and view from inside only. Joe Murgo is a scientist who answers questions. The email link is below if there are things you want to know which only Joe can answer.
"There are multiple reasons as to why the lightning can appear as different colors, some can be more complicated that others. Let me first start off as to why the majority of lightning appears white. Lightning is extremely hot, thousands of degrees, which can be equivalent to the temperature on the surface of the sun. Anything that hot will emit all different waves of electromagnetic radiation, including all of the main colors of visible light. The sun emits all colors equally too, and if we take away the effects of molecules of air, the color of this light would be white. Separated, we can see all of the colors of the spectrum like in a rainbow. An easy way to remember the colors of a rainbow is to remember the name Roy G. Biv. This stands for red, orange, yellow, green, blue, indigo and violet. (I like this info to help students remember easily) The Roy colors are of a longer wavelength and are created with a cooler temperature than the Biv. This is why an electric stove that heats will first change to a reddish color, but then turns white the warmer it gets.