Junko has a bright and bubbly personality, which is greatly reflected in the highly saturated and neon colors of her outfits. At this point she is trying hard to show her feminine side, which she had to hide from her most trusted friends.
Growing up, though, she developed a "cooler" attitude, as it's visible from her more desaturated and mature outfits. Here she finally accepted her dual nature, both feminine and masculine, by cutting her hair short and not being afraid to dress how she likes. She could wear a dress or a suit, it's not important if people misgender her.