In the aftermath of WWII, the Marshall Plan/ERP was promoted using propaganda posters, most of which displayed the flags of the nations involved. Which nation's flag is represented on the poster, linked to in the body of this post, with a single white fleur-de-lis on a blue background?

by AckbarsAttache

I know this may be better suited for a place like /r/whatisthisthing, but I figured the historical specialists here might have a better base of knowledge, since this isn't about a "thing" necessarily, but a representation of a historical artifact.

The specific poster I'm talking about is here: http://upload.wikimedia.org/wikipedia/commons/b/b3/Marshall_Plan_poster.JPG

I've done a fair bit of digging into the flag, and can't seem to turn up its identity. This is mostly just curiosity on my part, since all the rest of these flags are essentially the same today as they are represented on this poster. Thanks for your help!

Juvenalis

It's supposedly meant to be the flag of The Free Territory of Trieste, rendered in blue and not red, for whatever reason.

Source Wikimedia Commons and this page :

The flag of Trieste is blue colour, probably a mistake due to the fact that the Province coat of arms is blue and not red as the city coat of arms