I have a 9yo with a very strong sense of his style. He absolutely marches to his own drummer. In kindergarten, he put his foot down and told me I wasn't allowed to keep cutting off his hair, because he wanted to wear it long. It's now down to the middle of his back. We usually keep it in a long single braid, or sometimes two, because his hair is very very fine and tangles so easily. My favorite is when he puts it up in a messy bun; really suits his facial structure.
Also in kindergarten, he said to me, "I'm going to wear a cardigan every day!" and did so for the entire spring. Cardigans are still his favorite clothing article (must be all cotton, crewneck, button-front, in bright colours); we mostly shop the girls' section for these.
His preferred color palette is tropical brights; he's never been without a pair of bright orange pants (must be the Dutch genes coming through!), and loves colors like orchid, raspberry, and golden yellow. He dislikes graphics and logos for the most part, and was very insistent that I stop buying clothes with picture and patterns, but does make exceptions for hearts (his favorite motif), dogs, and anything astronomy-related. Stripes are okay if they are *rainbow* stripes.
He has accepted the fact that wearing pink and purple and having long hair will result in being mis-identified as a girl from time to time, and he appreciates it when the adults in his life gently correct strangers. He is somewhat non-binary in his outlook, much preferring to be referred to as a "person" than boy or girl, but doesn't like "they" for grammatical reasons, so is sticking with "he" for now. He has several gender non-conforming friends and classmates; so far I've found he and his peers to be very flexible, understanding and accepting of kids who aren't interested in upholding traditional gender norms. One of the things I love about parenting and teaching is watching them figure out who they are and how to present themselves in a cultural landscape that offers many more options than it used to.