"The sun in the Winter sets to South Southwest. This time of year it would not strongly backlight the plume. We would expect to see exactly what we saw."
Solar azimuth at 5:15 on 8 Nov 2010 in Los Angeles was 253 degrees. But it wouldn't matter if the sun set directly to the east. Clouds, contrails, missile trails...all appear white when exposed to direct sunlight at altitude. If the object filmed was climbing toward the sun, its trail would become white as it continued its track. Period. Like the picture of an actual missile launch below. 
Thanks for addressing the question I've ask since day one! (My first visual clue it was a high altitude aircraft -- not a missile launch from the surface...)
Probably one of the best photos I've seen illustrating the dusk sunlight principle I depicted in #537.
Why didn't the "missile" start off in darkness and climb into the bright sunlight?