Neat find. Arboga raises some interesting questions.
Arboga, California, is/was three miles South of Olivehurst. The community there was founded in 1911, and was so named by an unidentified pastor of the Mission Covenant Church of Sweden?for his home in Arboga, Sweden. The phrase "our colony" on the postcard?suggests the community might have been intended settlement for Swedish immigrants, but this is not borne out by other references I found in local newspapers. None of the references I found online give any more details. Apparently, the "colony" was more like a subdivision.
Arboga was later notorious as a temporary internment camp for Japanese Americans in WWII. Opened in May 1942, it was closed 53 days later when most of its inhabitants were relocated to Tule Lake (on the Southern Pacific's Modoc line). The Arboga camp was notorious for its unsanitary and miserable accomodations.