The two-tone cab option became a Regular Production Option on trucks in 1954.
Four different lower colors and an upper color of white/cream (and, 4 different "matching" two-tone interiors).
Looks like it was available earlier than that Tim.
Here is a picture of an earlier 47-53 cab on the GM assembly line.... clearly it is sporting 2 tones.
http://pic20.picturetrail.com/VOL1568/13678754/24528751/413967282.jpg.
