White is often associated with purity and peace in western cultures. The snow of winter is also very white!
White paper wafers were also sometimes used to decorate paradise trees. The wafers represented the bread eaten during Christian Communion or Mass, when Christians remember that Jesus died for them.
White is used by most churches as the color of Christmas, when the altar is covered with a white cloth (in the Russian Orthodox Church Gold is used for Christmas).
Blue
The color blue is often associated with Mary, the mother of Jesus. In medieval times blue dye and paint was more expensive than gold! So it would only be worn by Royal families and very rich people. Mary was often painted wearing blue to show she was very important.
Blue can also represent the color of the sky and heaven.
During Advent, purple and sometimes blue is used in most churches fort he colour of the altar cloth (in the Russian Orthodox Church red is used for advent).