At first glance it does look white, but it is actually a light grey or aluminum if you compare the color used to paint the white "Nickel Plate Road" lettering just below the "not white" stripe.
Here are a couple more examples.
|NKP Caboose 446 6-1964|
|NKP Caboose 1142 6-1964|
|NKP Caboose 1360 Chicago, IL April 6, 1957|
With out this turning into a "is the dress white/gold or black/blue?" type of debate, I hope you can see a difference.