Hi Martha:
When faced with questions about what to wear, I like to review the following very important rules. The first rule about fashion is that there are no rules about fashion. The first rule about Disney World is to dress in comfortable clothes and shoes.
In other words, wear your white pants with pride during your winter vacation in Disney World. They will not be "out of season." If it matters, I used to think Donald Duck was wearing white pants year-round until I realized he wasn't wearing any pants. If Donald can pull off the no-pants look, I'm sure you will look wonderful in your white pants.
Fellow panelist, and fashion inspiration,
Joel, even rocks colorful manpris (what some people refer to as clam diggers, pedal pushers, or three quarters pants) all-year-round, including winter, at Disney World.
Enjoy your vacation and white pants.