The colors red and green are complimentary, meaning they are on opposite sides of that color wheel you once learned in 2nd grade art class. These compliments have the greatest amount of contrast with one another, and when mixed with the proper portions of each can produce a shade of grey, one of which, being white: The Color Of Snow!
With that being said, may your Christmas this year be filled with the complimentary colors of red and green and fluffy white snow!
For now, enjoy this Christmas card from Pixar. Next year, I promise I will make my own. Hold me to it!