I have selected the colors based on the red and green of Christmas, but also the red and green of Phineas and Ferb's hair colors. The blue was chosen not only for depicting ice and cold, but also because it is a traditionally Jewish color and represents Hanukkah. Phin68 created our holiday logos and I think he did a great job with them. We even changed the colors on the main page so they didn't stick out so much.
Too much holiday cheer for you? Don't worry, we'll be switching back on Saturday January 3rd. Until then, you can always visit Special:Preferences and uncheck the box "Let the admins override my skin choice." and choose another skin. Smoke would probably be the closest to the regular PF skin. If you'd like, contact me and I will reset your skin to the regular skin.