Google has added multiple Easter eggs to Google Assistant, but this one is specifically for the Google Home. Tipster Ronald informed us that when you ask Google Home to "play Christmas music" or "play Hanukkah music," the alternating lights on the Home change colors. For Christmas, it alternates red and green lights, and for Hanukkah, blue and white.
I tried various other holidays, but was unable to find other color patterns. Still, this is a fun little feature, and I hope Google adds new tricks to the Home in the future.