Normally dark green, this succulent will turn red when physically stressed.

In this case, the stress is from extreme cold in our home's Solar Room.
The room is a large 12x80 feet and is totally enclosed by glass; including windows across the roof line. In normal Winter weather (with normal Winter temperatures), the sun heats the room & the temperatures will stay around 50 degrees at night. The only thing normally heating the room is this sun collection. On a really sunny, Winter day, it can get up into the 80's during the day. However, we've been having unseasonable cold with lots of grey days this Winter. Thus, this normally unheated living space has been under attack by the extreme cold outside its glass walls. Even with 3 space heaters now running full blast, it has been hard to keep our Solar Room above freezing.

Sadly, I've already lost several tropical plants. Cacti and succulents are more hardy and will tolerate cold better. However, even they are also feeling the stress. I raise the non hardy varieties. The softer, fleshy varieties (like this) are most vulnerable to cold.

It's suppose to be minus (-)11 degrees Fahrenheit outside again this week. Unfortunately, I have far too many house plants (many of them very large) to bring inside the main part of our home to wait until the weather moderates. I can only cross my fingers that the heat from the added space heaters does enough to save most of my Solar Room house plants. But if the succulents are now showing stress, the situation for my tropical plants is even more critical.