Now, I did some research and figured out why we did this in the first place, and it has to do with the color white keeping us cool in the hot summer days and not keeping the heat in during the cold winter months. It also had to do with the social classes and that it was rude when people who could afford extra leisure time in the winter months decided to rub it in because white clothing was symbolic of leisure.
While those rules don't necessarily apply today, I think there are some practical reasons we should not be wearing white (winter white is the exception, obviously) after Labor Day.
Fashion is all about tradition. While things change and things become new, there are staples in fashion that have never gone away. The classic LBD. A strand of beautiful pearls. Diamond earrings. These are things that never go out of style; wearing white after Labor Day should be honored for generations to come as well.
2)What if it snows?
If it snows, and you are stranded, you will blend right in. It may be a silly notion, but it could happen. If you are skiing or snowboarding (which, by the way snowboarding rocks!) you most definitely should not be wearing white on the slopes. We wouldn't want anyone to think you are a snow bank!
3) It looks funny
When I see someone wearing white after Labor Day, I think it looks weird. Fall colors are usually deeper and richer. White is neither of those two. White looks and feels summery. White dampens the mood of the rich fall and winter colors. If worn after a snow fall, it can make it seem like you are trying too hard to blend in with the scenery. We are made to stand out, but also to work with our surroundings.
So, those are my three main reasons to not quite wearing white during the fall and winter seasons. Keep to our forefathers and foremothers traditions of fashion--don't try to fix what isn't broken. Don't be silly on the slopes--you could get injured. :) Lastly, it looks silly--Stand out and work with your environment.