I barely know color theory and I'm an "artist". I do like clothes though... I don't know what your environment limits so you can take or leave what I say here.

High-waisted bottoms can create a really nice femme silhouette. Tucking a t-shirt into some high-waisted pants is an instant look. For bottoms, black is always a great color but I also love the look of brightly colored long pants too, I think it's super fun.

I love tank tops. There are many different styles. I often make my own by cutting sleeves off of t-shirts because I'm really into DIY, but idk if that's something you're interested in. I searched up "tank tops" on Temu and I'm seeing some cute stuff in the women's section. If you don't like showing skin, tank tops make a great underlayer. Tank top + button-down short-sleeve is a classic nonbinary look imo.

On that note, short-sleeve button downs! Especially if they're a bit oversized and baggy? Fantastic look. Again, seeing some cool shit in the Temu women's section.

I also really like billowy, light blouses. There are a million different styles of blouses to choose from in women's clothing and not all of them are even overtly femme. A super light blouse is also really good for being in hot weather but also covering a bit more skin. I personally am a fan of blouses with really drapey, flowy sleeves. Blouses also come in so many fun patterns. The world of blouses is infinite.

Also, a nice, slouchy cardigan or two is always helpful. Can instantly tie an outfit together. I prefer my cardigans oversized and comfy.

For patterns, I love everything plaid. I also really like pinstripes, I find them really flattering. Sometimes I like checkers too, but I'm way more picky with that. Plaid is forever. I also don't think you have to worry too much about color-picking when it comes to clothes; most colors go with each other. And a lot of people love pattern-clashing in outfits.

I DIY a lot of my clothes and I could go way more into that, but I left it out of this post. If anyone is interested in that, lmk!