See your flash or camera instruction manual for more details on fill-in flash. A snowy background can provide the perfect setting for getting some dramatic results. Or with slide film, you can get the romantic, ethereal effect of a seamless dreamlike background when you slightly overexpose a person in the foreground and let the detail in the background disappear altogether. Also, you can slightly overexpose a winter scene on a slide film to produce a soft pastel rendition of the scene- especially early or late in the day. If you underexpose a scene just a bit with slide film, you'll get intense saturated colors, heightening the isolation of colored subjects.
Sunlight offers other interesting possibilities.
When these colors dapple a wintry landscape, the results can be stunning. Shadows are softest at these times of day, too. Sunset and sunrise offer an exciting and unpredictable fairyland of colors from pale rose to fiery reds and oranges. Midday is probably the most colorless time of day, so look for subjects that are inherently colorful. You can also exploit lighting direction for dramatic impact.