It's funny that you mention this. In the latter part of my childhood, my family moved into a town that is characterized in my city as WASPy. Being around true WASP/Preps, you learn the different nuances that separate them from white people that try to imitate their lifestyle. One of the things that I noticed with respect to the way they dress is that the khaki pant is their staple pants. Even more, you will notice among those that are authentically wasp/prep, that they don't ever wear blue jeans. And in fact, there is a style rule among them based off of what you just mentioned. The rule is "a gentleman never wears blue jeans". It's based off of the fact that the Lee Dungarees (which I believe were the original blue jean) was adopted by the cowboy who were wild frontiersman, cut from a different cloth from the more sophisticated New England or Tidewater aristocrats whom were considered "gentleman". Gentleman were thought to wear khakis, while the uncouth frontiersman wore blue jeans. To this day, when I'm around certain authentic upper class circles, you will never see them where blue jeans. Which is why they don't wear fashion brands like Ralph Lauren because, in him trying to imitate their lifestyle, he misses out on a lot of nuances, like wearing or including jeans in his looks when jeans was looked at as being beneath them.