Chocolate brown and black are good colors for bridesmaid dresses when you are getting married in the winter. Other warm tones like deep red or orange are also good, but they can look to fall-like if you are not careful. Stay away from pastels and colors that are too bright.
If the winter wedding will be in an area with snow, i like the idea of using a nice shade of blue for the bridesmaid dresses. Or you can do it more along the lines of Christmas and use red for the bridesmaid dresses.