The Thermograph or Heat Map tool (taken from the technique of the same name) remaps image colors using luminance as an analog for heat. Cooler temperatures are rendered in blue, while hotter temperatures approach fuchsia.
(Every release, the PhotoDemon developers include a few “Experimental” effects. These are typically strange or not-easily-classified filters that may or may not be useful, and we’re curious to see if people like them. Depending on feedback, they may be developed into full-blown tools, or dropped from subsequent releases.)