OK–as a Canadian modeler I should know this, but I don’t. Back in the 1970s and '80s many CN 40- and 50-ft boxcars had their doors painted various colours–I remember yellow and green. I assume that this was to identify the service or cargo for which those cars were intended. What did those colours mean, and were there any others besides green and yellow? As always, thanks in advance.
Yellow and green were the only colours I recall, with green representing cars in lumber service, while yellow was used for those in newsprint service. Ontario Northland also ran some newsprint-service boxcars with yellow doors, while the cars themselves could be either medium green or boxcar red.
Wayne
Thank you Wayne. That means that my recently acquired green-door boxcar will fit right in!
I remember reading an article somewhere about this, but I am afraid I don’t remember where…darn the ravages of time! 
But, I do remember reading that CN also had blue and red doors as well. And, I have seen them in various states of fade and dirt rolling by. However, I don’t recall what the colors denote.
Hope this helps
You are absolutely right, Sorarail, except that you are thinking of mechanical reefers. I have no memory of them myself, but I did a bit of digging and confirmed that yes, indeed, many CN mechanical reefers had blue or red doors. The cars themselves were silver and the doors could be silver, blue or red. I don’t know if the colour of the door indicated some sort of mechanical feature or the designated lading, but the one car I found with a red door was lettered “For fresh produce only”. CN’s mechanical reefers also came in basic reefer yellow with black lettering, similar to BNFE cars.
I know the yellow door boxcars shipped newsprint, but were the yellow door cars newsprint service only, or did it stand for clean lading only (which would include newsprint but perhaps also grain and other more delicate loads)?
Dave Nelson
There’s a little info on CN newsprint service boxcars HERE, although it doesn’t give AAR codes or mechanical designations for any of these cars. I don’t have a recent ORER to look-up their class, but I’d guess them to be XL or XP type, and suited to solely to newsprint service.
Wayne
CN door colours:
Yellow: Newsprint/Paper
http://canadianfreightcargallery.ca/cgi-bin/image.pl?i=cn561800&o=cn
http://canadianfreightcargallery.ca/cgi-bin/image.pl?i=cvc402958&o=cv
http://www.cnrphotos.com/gallery2/main.php?g2_itemId=21766
Green: Lumber
http://www.cnrphotos.com/gallery2/main.php?g2_itemId=25129
Blue: Mechanical Refridgeration
http://www.cnrphotos.com/gallery2/main.php?g2_itemId=21721
Red: Produce service? (Ice reefers)
http://www.cnrphotos.com/gallery2/main.php?g2_itemId=16826
Orange: Express service (boxcars/insulated cars, less common)
Colour coding officially began around 1960 and ended by the early 1980s, although there are still the odd cars out there that haven’t had their doors repainted. (This also applied to paper and lumber boxcars from CN’s subsidiaries Central Vermont and Duluth, Winnipeg and Pacific.)
CN’s regular boxcars are painted brown; refrigerated cars were painted silver/gray.
The only ones I’ve seen in those colours were the ones leased from North American and originally bearing NIRX reporting marks. (Cars were later renumbered CN.)
http://www.cnrphotos.com/gallery2/main.php?g2_itemId=50847
Insulated, but not refrigerated, cars were painted standard CN brown. (These cars were also usually equipped with vents and heaters.)
Thanks for all these replies–I’ve learned a lot!