Interesting. Their technical people told me over five years ago that the silver chanssis was softer because of the additive necessary to turn the plastic silver, while the carbon black in the black chassis did not act as filler and resulted in a stringer, slightly denser product.
Speaking from experience as someone who works in the plastic's industry. If you call surfing RC car web sites all day work. The darker or brighter the color of plastics the stronger. When we mold the exact same part in different colors the black parts are always stronger. I really don't think there is "much" of a differences between black and silver but there is some. And with the way I drive I can break parts in any color.