As a matter of fact the first four days of the Christmas Season, the vestments alternate white,red,white, red. Today we use red because we celebrate St Stephen, the first martyr.
It may at first seem odd that on the second day of Christmas, as we celebrate the birth of the Lord, we jump to the other end of the spectrum, and celebrate a gruesome death.
It all makes sense when we remember that for us death isn't death, at least, not in the sense of "the end." Early Christians used the phrase dies nalatis, literally birthday, not for the day you were born into this life, but the day you entered eternal life.
We celebrate the Birth of Jesus followed by the Birth (into eternal life) of St. Stephen. Something to ponder as we think of all those who have had or will have loved ones pass into eternal life during the Christmas Season.