In April, 1939, Hoffmann did a whole series of “test photos” of Hitler dressed in his new white uniform. He started wearing it in May, 1939. This photo was taken July 21, 1939 and was another “test sequence,” this time for a brown uniform he’d been wearing for 6 years.
Possibly Hitler wanted to compare the white jacket with the familiar old brown one. This is Hitler’s Arbeitszimmer at the Berghof.