Is the beautiful blue Danube blue? Slonimsky reports that someone in Vienna watched it for an hour every day for a year to note its color. It was green 255 days, gray 60 days, yellow 40 days, brown 10 days, and not once blue. According to a letter to the New York Times in 1945, it was, in fact, blue upstream from Vienna. Was it blue in Vienna when Strauss wrote the waltz? How far upstream do we have to go to see it blue today?