This street was created in 1895 as part of the plat of Seattle’s tide lands. As Seattle expanded to the south, it became obvious that Commercial Street (1st Avenue S) would not be the westernmost street east of Elliott Bay. Fortuntately, instead of using zero or negative numbers, they went with states: the first street west of 1st was named Utah, and the next, Colorado. (Some perpendicular streets were named Alaska, Vermont, Connecticut, Texas, Massachusetts, etc. There doesn’t appear to have been any particular order.)
Colorado Avenue S begins at S Royal Brougham Way and goes ⅓ of a mile to S Massachusetts Street. It begins again on the back side of the Starbucks Center and goes ⅘ of a mile to just south of S Spokane Street, and its final segment begins just north of Diagonal Avenue S and goes ⅔ of a mile to S Dawson Street.