Anyone interested in American city flags should have a copy of the book of that title: American City Flags: 150 Flags from Akron to Yonkers, by John M. Purcell with James A. Croft and Rich Monahan, published in 2003 as a special issue of Raven: A Journal of Vexillology by the North American Vexillological Association (ISBN 0-9747728-0-1; PDF here). It contains a wealth of historical material, including this item about the earliest attempt at a flag for Portland, Oregon:
In 1917, Mayor Harry R. Albee appointed a committee to ascertain if Portland needed a flag to accompany its new slogan, “Your Portland and Mine”. The committee examined the flags of 31 other prominent U.S. cities and determined Portland should have a flag, appointing Morris H. Whitehouse to lead a flag design contest. Having published extensive specifications, the committee received several proposals. Design number 8, by H. W. Frederick, won first place and $25. It is a horizontal tribar of equal white, blue, and white stripes, the blue stripe representing the Willamette River. A red circle centered on the blue stripe represents the city of Portland. However, the committee found that the best design did not measure up to the standards outlined in the contest guidelines. The flag did not appear to have “certain important requisites, such as historical association dating back to the earliest periods of the city’s history”, as Whitehouse made clear in the specifications. The flag did not express any apparent “robust civic ideal” or “common aim and purpose”, nor did it convey “civic spirit”. Joining the patriotic fervor of World War I, the committee recommended that Portland instead fly the Stars and Stripes for the time being. The Frederick design was never adopted. (From the chapter on Portland, Oregon by Mason Kaye)
Portland Flag Association 
Not a bad design, I say, despite the color-on-color. Those “important requisites” sunk the contest boat before it was launched.