Thermochromic material for low temperature?
I found a supplier of raw thermochromic pigment active in the temperature range you are looking for. But to make it into paint you would have to add binder yourself.

Company is called Shenzhen Yu Mingjie Pigments Co., Ltd.



Has different thermochromic pigments active in the ranges -5C to 78C

Be sure to specify the temperature range you are interested in.