"The Christmas Episode" finds Ricky and Lucy Ricardo and their friends and landlords, Fred and Ethel Mertz, decorating Lucy and Ricky's Christmas tree and reminiscing about how their lives have changed since the arrival of the Ricardo's son, Little Ricky. Flashbacks (in black-and-white to emphasize the time lapse) recall the night Lucy tells Ricky she is pregnant, the time Lucy shows up unexpectedly as part of a barbershop quartet, and the day Ricky and the Mertzes rehearse taking Lucy to the maternity ward. (details via: CBS Press Release)
The episodes have been colorized with a vintage 50's look - so it still will have that retro feel.
Also, the "I Love Lucy" Christmas Episode is available in an all new DVD release:
I Love Lucy: Colorized Christmas