There were two different 'single lightning bolt' symbols.
The second one has different colors and is portrayed on a flag. What's its meaning?
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This particular symbol and color combination would be the Deutsches Jungvolk in der Hitler Jugend (German Youngsters in the Hitler Youth).
The Deutsches Jungvolk in der Hitler Jugend (DJ, also DJV; German for "German Youngsters in the Hitler Youth") was the separate section for boys aged 10 to 14 of the Hitler Youth organisation in Nazi Germany. Through a programme of outdoor activities, parades and sports, it aimed to indoctrinate its young members in the tenets of Nazi ideology. Membership became fully compulsory for eligible boys in 1939. By the end of World War II, some had become child soldiers. After the end of the war in 1945, both the Deutsches Jungvolk and its parent organization, the Hitler Youth, ceased to exist.
The emblem of the DJ was a white Sieg rune on a black background, which symbolised "victory". This was worn on the uniform in the form of a cloth badge, sewn onto the upper-left sleeve of the shirt.
The 'flag' or banner shown in your question's second image fits the description of the badge/decoration used by this younger division of the hitlerjugend. This fits with the age of the title character