I used to instruct at a major Midwest university flight school.
Pre Solo Student pilots wore a blue shirt with epaulets.
Solo Student Pilots wore dark blue shoulder boards without stripes.
Private pilots wore dark blue shoulder boards with one silver stripe.
Instrument pilots wore dark blue shoulder boards with two silver
stripes.
Commercial pilots wore dark blue shoulder boards with three silver
stripes.
CFI pilots wore dark blue shoulder boards with four silver stripes.
Instructors wore white shirts with black shoulder boards and three
gold stripes.
ATP instructors wore white shirts with black shoulder boards and four
gold stripes.

Students wore dark blue slacks, black shoes or boots.
Instructors wore black slacks, black shoes or boots.
White tennis shoe were not permitted.

Hair neatly trimmed and no jewelry other than a watch or ring.

Conduct while in uniform is something to consider. Do not be like the
Dean Martin / Foster Brooks bar video. It is funny but not the thing
a pilot should do while in uniform.

If you do not want to wear a uniform, don't. If you dress in a nice
polo or button down shirt, slacks or jeans which are in good repair,
no one will look down at you at the airport. Don't even go to an
airport wearing nose rings, earrings, Grateful Dead t-shirt, long
nasty unkept hair, faded blue jeans with rip holes, John Lennon
sunglasses and Jesus sandals. Not only will you not get any respect
but the TSA agents or local law enforcement may escort you to a small
private room for a chat.

Nothing wrong with looking the part but try to dress in a manner which
blends in with the rest of the pilot community.
Each airport has its own flavor of pilots.