Annie Rauwerda writes Siamese cats are heatmaps of themselves:
Siamese cats are walking heatmaps. Their characteristic coloration results from a delightful mutation (maybe I should call it a mew-tation) in tyrosinase, an enzyme that makes melanin. A deleted cytosine amino acid causes a frameshift mutation. The result? Tyrosinase in Siamese cats is particularly sensitive to temperature, denaturing at normal body temperature.
This means that near the cat’s warm body, the enzyme doesn’t function, and melanin isn’t produced. But at colder extremities like the tail, feet, ears, and face, the color kicks in.