stuck on M3 today as a result of the pileup and was watching the fork lightning a spectacular show. Then suddenly there was a massive slow motion bright blue fork lightning across the sky. Never seen it blue before been fasinated with fork lightning for years, [cannot watch the flash lightning hurts my eyes and gives a headache].
"It depends a bit on the angle of view and dispersion of he light, just as dust makes sunset and sunrise go to the opposite end of the spectrum."
Sunsets are red for two reasons. When the sun is near the horizon the light has to travel through more of the earth's atmosphere before it reaches your eyes, and the dust that is present scatters more of its light, until less of the shorter, blue wavelengths get through. We end up seeing the long wavelength, red light.
Angle of view doesn't have anything to do with what you see in a lightning flash. That looks blue-white because nitrogen is being excited by the enormous energy flow. The blue-white color is caused by light emitted as the electrons drop back to their original energy states.
Dust in the atmosphere can certainly cause colour tinges in lightning, as morddwyd suggests.
"I sometimes see a blue tinge in some car headlamps"
There are automotive bulbs available with a blue tint. Some are very blue, others less so. The Xenon lamps some people fit are very blue/white and bright and depending on the type not strictly legal, and will often result in MOT failure. My young neighbour has them and puts his ordinary bulbs back when his MOT is due.
I have some Osram 'Nightbreakers' in my headlamps which have a blue band around half of the bulb. These lamps are slightly overrun which makes them brighter and the blue tinge makes them appear whiter. The downside of them is a slightly shorter life but so far this hasn't caused me any problems.