What statement about spot suits during the 1930s is true?

The statement that spot suits became mainstream during World War II is accurate because, as the war progressed, styles began to shift and incorporate the more flamboyant and expressive elements from jazz culture into everyday fashion. Before this era, spot suits, with their bright colors and bold patterns, were primarily associated with jazz musicians and performers who sought to stand out and make a statement on stage. However, the wartime environment encouraged a more adventurous approach to fashion, leading to the acceptance and popularity of spot suits among a broader segment of the population, not just within the jazz scene.

This transition reflects how music and culture can influence fashion trends, demonstrating jazz's strong impact during this period and its evolution as the nation adapted to changing social dynamics. In contrast, the other statements do not hold true because spot suits were not confined to Harlem, nor were they widely disliked. Additionally, although spot suits were notably worn by jazz musicians, they were not exclusive to them, as other groups began to adopt this style during the war.