I'll go out on a limb and guess that the intent was to eliminate any possibility of similar jersey colors between opponents...for example, if my dark (away) jersey is black and my light (home) jersey is a light gray, and my opponent's light (home)jersey is white and their dark (away) jersey is a darker gray, we are going to look mighty similar when playing at my place.
Also, it eliminates "Argentina" style jerseys with equal stripes that are used for home and away...works OK until you run up on another team in the playoffs that had the same idea.
No inside information, but that just sounds reasonable for the intent of the rule...
Now, a little colored piping or cuffs/collars on an othewise solid-white jersey...your guess is as good as mine. I will wait for wiser minds to elaborate.
