Some aesthetics with bright colors similar to Rainbowcore include...
Harajuku Decora: Decora is a Japanese aesthetic and fashion style that revolves around an excessive amount of accessories, primarily focusing on plastic hair accessories and bracelets. The origin of Decora can be traced back to the popularity of Japanese idol Tomoe Shinohara among teens during the 1990s. Decora fashion is characterized by its bright colors and bold patterns, often incorporating elements of kawaii (cute) culture and Harajuku street style.
Kidcore: Kidcore is an aesthetic that centers around bright colors, nostalgia for icons from the 90s, and kid themes. While its origins can be traced back to the 70s, 80s, 90s, and 2000s, it appears the aesthetic is a nostalgia-based creation of the 2010s. Decora fashion has influenced this aesthetic, although Kidcore is less over the top and focuses more on childhood nostalgia and bright colors. Kidcore differs from Babycore as it is more focused on bright colors, cartoons, nostalgia, toys, and accessories, as opposed to soft pastels, stuffies, soft kawaii fashion, and baby items.
Both Harajuku Decora and Kidcore aesthetics celebrate bright colors and playful elements, making them similar to the Rainbowcore aesthetic.