The Poppy Field was one of the highlights of the show, and the finale of Act One. In the tinted color postcard, we see (from the left) Sir Dashemoff Daily (the Poet Laureate) and Dorothy meeting up with another group of characters - Pastoria (the exiled King of Oz), his fiancee Tryxie Tryfle, the Lion, and Imogene the cow. They are disguised as a one ring circus! As you can see, there are a number of characters in the show that are unfamiliar to fans of the book or the movie. The Poppies were portrayed by chorus girls, with large flower hats, who sang and swayed as their scent overpowered the travelers.
In the second postcard, the Snow Queen is seen and the Poppy Field has been destroyed by snow - a device that was re-used in the 1939 MGM film. On stage this was achieved in a transformation scene, a quick change from the live poppy field to the frozen flowers.
The "handwritten" inscription on the color postcard was actually printed as part of the card - I've seen it on at least one other example, beneath a different image. A bit of advertising for the show!