One who says they study rainbows supports the LGBT+ community, is highly educated on sexualities, gender identity, etc, and strives to raise awareness on the subject.
This phrase became popular to use after Harry Styles tweeted "I study rainbows".
Sunshine Lollipops and Rainbows is a song made by Leslie Gore that anyone could like, well unless you are a Norwegian communist that wears a red hoodie, wears a Band-Aid on his face, has Horn-like Hair, and is obsessed with Giant robots, then you would be pissed why its playing.
An expression referring to a very happy, care-free life where you have just about everything you want. It can also be used to refer to a place where someone's life will be happy, fun, and easy. When using it for children or to refer to children, it means innocence, happy, playing, loving childhood.