Like normal cameras, most Thermal Imaging cameras offer you the choice of Auto or Manual, which controls how the colours (of your chosen palette) represent temperature:
In Auto the colours are spread over the range of temperature then in view, which will automatically adjust when hotter or colder objects are seen by the camera. Auto is simple to use, but the colour corresponding to a particular temperature changes dramatically when extreme temperatures come into view. For example when a hot radiator or cold sky comes into shot.
eg: this Auto Flir One 10 sec video clip shows two terraced houses on a frosty morning: one on the left has solid brick walls, while the right-hand one has insulated cavity walls, loosing less heat. Notice what happens to the colours when the cold sky (-40°C) comes in and out of view:
When Manual (or ‘Locked‘ for Flir Cameras) is selected, the colour representation of temperature at that time is locked. If hotter or colder objects come into view, they are usually shown as white or black (for too hot or cold). Manual (or Locked) mode is useful for comparisons, with each colour continuing to represent a particular temperature.
Here’s the previous video, taken again with a Locked setting:
Both Fluke and Flir offer software that can retrospectively adjust how colours represent temperatures (and a lot more).