General: Navy is definitely my favourite colour. Beyond that it's probably charcoal gray, brown. Black can be nice for the right item, I generally avoid bright colors like pink, light blue, yellow, red, and I'm not a fan of white or beige.
Collar: I like the "band collar" style. I also quite like the style that has multiple layers & kind of looks like another jacket inside it.


Zip/Buttons: I like minimal fuss here - when the buttons/zip are covered up is best. Don't like buttons that draw attention to themselves
Length: I much prefer just-past-waist-length. Don't like too long and also don't like too short
Other: Not a fan of the bomber jacket style. They don't go without enough things & constrain what else you can wear.
My favourite kind of t shirt is definitely just a plain collared polo. I'd love to find somewhere online that I can reliably buy high quality, nice fitting, reasonably priced, collared polos that don't shrink in the wash.