Thanks very much for the suggestions and links.
I realize that the following will be obvious to you, but it shows where I'm at on my learning curve:
My last camera was a Rebel XT and all my indoor photos were made using its popup flash. (I also often used the popup outside and in back-lit situations.) Other than that, I never really gave much thought to lighting and never considered the colour of indoor light.
Along comes the 6D, happily taking pictures without flash in very low light situations- producing useable photos at ISO 12,800. Useable, but who knew that the type of lighting would so dramatically affect the colour and tone of the results. D'oh!
The effect was pleasant with the LED lights of a Christmas tree early one morning, but I've developed a dislike for incandescent bulbs. Two of those mounted in wall sconces cast an orange-brown glow on a whole series of extended-family Christmas dinner shots, ruining the photos, although maybe I can fix that in photoshop.
The 6D has provided other surprises- it's pretty happy under fluorescent aircraft cabin lighting, at least during the day. Shots that ALWAYS required fill flash in the harsh contrasts of flight deck lighting are possible using the automatic HDR backlit setting. But- what I'm really looking forward to- door-off-aerial in a Cessna with my first full-frame- will have to wait, 'cause even for a canuck- it's way too friggin' cold to even think about that before April...