I agree with the idea of danger linked to the yellow color, the "scabs" in a strike situation were and are still maybe called "jaunes" "yellow" in France. There is an " avenue de la Porte Jaune" in Paris but I've not yet found out why. But not every culture has that idea about yellow , by Google searching "portes jaunes" I found this in Hue Vietnam http://www.pacificvietnam.com/.tours/highlight/Fascinating%20Vietnam.htm NGO MON GATE : this is the principal entrance to the Imperial Enclosure and faces the Flag Tower. The central passageway with its yellow doors was reserved for use by the emperor, as was the bridge across the lotus pond. Luc