Back when CN was still a Crown Corporation; I recollect it was normal for freight equipment to be lettered Canadian National on one side and Canadien National on the other. It would make perfect sense for a CN theater car to carry bilingual identification as well.
Since the photos don’t carry dates; it’s possible the lettering was yellow at one point and white another. Were it me; I’d choose one color or the other and run with it.
Curt
Edit: I Googled CN theater car Sandford Fleming and found a right side photo of the car with yellow lettering. Following is the link to the photo. Based on this and other photos; it’s apparent the car had different paint and lettering schemes while owned by CN.