Plus, the red would clearly differentiate it from the black and white German cross at a distance.
Depending on what the USA uses, I could also imagine a Confederate roundel being similar to the 1941-43 US roundel...A white star in a blue circle outlined in a red circle, perhaps with a thin white line separating the blue and red...or a red square with the white outlined bue circle and star within...or the Tennessee flag.
White might also be a major element of the CSA roundel - the last two national flags featured white as the dominant color - plus one can't ignore the racial connotations of a white roundel. Why not a simple blank white circle, with a thin red line on the edge and a thin blue St Andrews cross in the white circle...or just a white circle with thin red on the outside.
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