If you use Goggle Image and look at photos of lightning, you will see that it is white, often surrounded by either pink, blue or green "flash."
When I paint it I usually make the "flash" or fuzzy outline out of pink or blueish-green, sometimes purple, and then add the white "bolt" over the top of it. However, in this one, a watercolor, I masked the lights and the lightning, and painted them in later. . . .not quite as effective: http://i266.photobucket.com/albums/ii267/art4now/100_1572.jpg (This was a very experimental piece.)
