I'm not much of a fan of "O", but the company's dress code is pretty simple and not hard to follow.

"If not traveling in uniform, the following dress code applies:
First Class
Males: Dress slacks and dress shirt (tie not required) or turtleneck. 
Females: Dress, suit, slacks / skirt with coordinating blouse.
International: Business casual attire
Coach Class
Males: Casual slacks with collared shirt/turtleneck and casual shoes with socks.
Females: Casual slacks / blouse / sweater and casual shoes for females.
Unacceptable Clothing for Deadhead or lnterline Travel:
Sheer / strapless / thin strap tops
Sandals /thongs
Athletic-type shoes.
Denim fabric / jeans.
Shirts with no collars.
Jogging / sweat suits.
T-shirts / tank tops.
Shorts / cut-offs.
Mini-skirts."