Printing parts of my sign for the exterior of the makerspace. I noticed that this thermal reactive filament (which turns yellow when hot, green when cold) was cooling rapidly at this end. I was printing pretty quick (450-600mm/min travel), but it’s pretty neat to see the effect represented.
Useful for finding your cold spots!
It is, I’ve just never seen thermochromic filament cool below its color change temperature while still being printed. Usually the heat rising from the bed plus that retained by the print’s own mass was more than enough to keep it at is’t “hot” color.
Its because it doesn’t get below 40 in Cali 
I have to warm my space up to at least 50 before I can reliably print.
True. If it’s that cold in the room, the printer will throw mintemp errors and refuse to heat up because it thinks its thermistors are disconnected.
Yes I noticed that pretty early on when the snow started falling. Luckily my space is relatively small so its not a big issue to heat up.