Update

I've found a lot information that I've been reluctant to share until now.
I guess the best ways to organize it will be to answer the questions I've been asking myself.

What's a "World's fair?"
Here's a modern definiton
that's seems consistent with it's historical meaning.

What's the significance of the word "Colored?"
It was an attempt to define a group according to prevailing theories of "race" while including people who weren't former slaves, weren't from the United States, and/or had "interracial" ancestory.

What's a "Display Trailer/Trail car?"
While I've found examples of modern mobile "display trailers" that can be used at fairs, I've found no evidence of "display trail cars." However, all the plans I've found for the various "World's Fair" all show stationary buildings.
This leads me to suspect that the phrase refers to a display of a trailer/trail car.

What's a "trail car?"