The word “Christmas” is a simple contraction of “Christ’s Mass.”  It is a reference to the festival Eucharist which is traditionally celebrated on the occasion of Christ’s nativity.
The celebrations of Christmas and Epiphany were both associated with the Winter Solstice (that celestial point where daylight hours are at their shortest and wherefrom they begin to lengthen).  But, because of the inaccuracies of the ancient calendrical systems, the Winter Solstice was recorded as occurring on January 6 in 1996 BC and later recorded occurring on December 25 by 331 BC.  The reason for Christmas and Epiphany being linked with the Winter Solstice is that (once Christianity became the dominant religion of the Roman Empire) the celebration of Christ’s nativity supplanted the celebration of the birth of the pagan god Mithra.  The celebration of Mithra’s birth was observed on December 25 (what was then believed to be the Winter Solstice).  With the decline of pagan religions, Christianity inherited (by default) December 25 as Christmas day
That “Christmastide”—the season of Christmas—consists of twelve days is well known from the old English Carol, “The Twelve Days of Christmas.”  Eventually, the observances of Christmas and Epiphany became differentiated, Christmas day being linked to December 25 and Epiphany being linked to January 6.   Christmastide becomes a twelve-day season (December 25 – January 5) as a result of distinguishing the observance of Christ’s nativity (Christmas day) and the visitation of the Magi (Epiphany).
The liturgical color for the season of Christmastide is white.  White represents the holiest of days in the life of the Church because it signifies the glory of our incarnate Lord, Jesus Christ.  White symbolizes purity, holiness, and virtue, as well as respect and reverence.  White is used for all high Holy Days and festival days of the Church year.  It is indeed proper and fitting for us to mark the season of Christmastide with the holy color of white.