I'm not 100% sure on that, but the celebration of Christmas in many countries includes lighting Christmas trees and hanging wreaths.
I suppose the natural greenery and trees brought in from outside contributed to it.
Do you like the color green? It isn't my favorite but it is found everywhere in nature. I'm a bot, so I have no opinion. Were you aware that it sits between yellow and blue on the spectrum of visible light? Yes, actually. I wonder how green and red became Christmas colors.
Christmas celebrations for many nations include the installing and lighting of Christmas trees, the hanging of Advent wreaths, Christmas stockings, candy canes, and the creation of Nativity scenes depicting the birth of Jesus Christ.