"You can't wear white shoes (or pants, or skirts) after Labor Day!" I think that everyone has heard this rule, and most of us follow it. It makes sense - white linen pants look horrendously out of place in November. However, sometimes white can look utterly right during the colder seasons.
For instance, picture a soft chocolate brown cashmere sweater or a teal velvet blazer with a pair of crisp white pants, or a sleek white pencil skirt with a black turtleneck. Both of these could work in the fall and early spring. What matters is the material of the white item in question - it must substantial, no chiffon or linen. Also, keep the color on top, and your accessories, dark and wintry, or else you'll look too out of place. Of course, white on top is perfectly acceptable year round.
What about your favorite white leather bag (this can also apply to pale pink, baby blue, or any other summery pastel)? It might look great contrasting with your black suit. This look only works with bags made of heaver materials like leather, croc, or microfiber. Do not bring out woven or straw bags in January.
White shoes, however, just don't work out of season. Many styles are too flimsy for winter wear to begin with, and shapes like pumps and boots are just bad and kind of trashy 99% of time. (My one exception would be white pumps with a flowy sundress or light-colored palazzo pants in the summer. And there is never a good time for pure white boots.) Winter white, ivory, or cream colored shoes can work, though, just make sure you stay out of mud and slush, because nothing is worse than dirty white shoes. And of course, never wear black hose with light colored shoes.
Don't feel the need to put away your favorite white pieces just cause its Labor Day. Do put away anything linen or made of straw, however. Just don't be afraid to break the "rules" of fashion. After all, if Coco Chanel, Mary Quant, and Christian Dior hadn't been afraid to challenge the established looks for women, where would we be today?