In the first book, "The Wonderful Wizard of Oz" (1900), the walls are green, but the city itself is not. However, when they enter, everyone in the Emerald City is made to wear green-tinted spectacles. This is explained as an effort to protect their eyes from the "brightness and glory" of the city, but in effect makes everything appear green when it is, in fact, "no more green than any other city". This is yet another "humbug" created by the Wizard.