Svea Livgardes Marsch [Swedish King's Guard March] 

It might be, interesting point!

No, it's most probably the Swedish flag. The colour sensitivity of film back then was different.

Its the Swedish flag. At the time when the film was made the film emulsion was only sensitive to blue light, so called orthochromatic film. This meant that anything with blue in it would become practically white on the film, while anything else would become darker greyscales.