check out this link:

http://www.xframechevy.com/tarrytown-ny-assembly-plant-1959-chevrolet/

about 3/4ths down the page you can see engines being offloaded from a box car and being prepped for installation. The 6-cyl are blue, and both the small blocks and the W-series big blocks are orange. Even though there are trucks shown on the assembly line (a yellow 59 big bolt is shown), there are no gray engines seen.