fwiw: I called Lionel service this morning and explained the color variations...the cordial customer service rep was able to see the difference in blue colors. He said he will check and get back to me. I encourage everyone else to do the same. The thought of returning my RPO cars to my dealer occurred to me, but I will wait until Lionel gives a reply.
I also checked my scale heavyweights as well as my traditional sized PE coaches, and they are all a deeper shade of blue.
Someone expressed to me privately that the RPO "powder blue" color as I call it, may be more representative of the actual PE car portrayed in the movie and/or book. In my opinion, this is a remote possibility. But, before I chalk the color mix-match up to a gaffe on Lionel's design or production, it should be verified, however I don't have the time right now to do so. If I don't hear back from Lionel within a week, I'll give them another call.