I would say don't wear white pants period, before or after Labor Day.
Seriously. I don't want to know what brand undies you wear, and so many white pants/dresses/skirts are not lined. I don't care if you're wearing "nude" undies - chances are we can probably still see them.
Bra straps aren't cool, either. Cover up and wear appropriate foundation garments, people!
Threaded Mode