I missed last week, but now I’m back in the saddle today with an extra-long one.
A medieval knight in full armor was closer to overheating than freezing. A suit of armor is a metal box with as few large openings as possible, because every hole to let heat out could also let something sharp in. According to those who still wear armor today, that can be kind of nice in the cold. In the heat, though, it would have been miserable, combining trapped body heat with absorbed sunlight to make something decidedly uncomfortable. As one poster on that forum writes, “In warm weather, you just sweat profusely until everything is soaked.” Delightful.
Being a true white knight might have helped a little bit in direct sunlight, which would bounce off white armor instead of being absorbed by it. But white armor also wouldn’t radiate body heat away as effectively as darker armor would, so it would be better at keeping everything inside the armor (namely: You) at a constant temperature. That might make it something of a wash.
This effect is also entangled with a thorny issue within evolutionary biology: Countershading. Most animals have dark backs and light bellies (except a few who live life upside-down and have dark bellies and light backs). The common explanation of countershading goes back to Abbott Thayer taking pictures of dead birds and hypothesizing that countershading is for camouflage. (He actually proposed two related but distinct ideas that are popularly squashed together because people like simple stories). But experimental biologists have found that countershading doesn’t always help an animal camouflage—in one experiment, creating fake insects with lard and flour, countershading half of them, and seeing which were more readily eaten by birds.
Countershading doesn’t always help with camouflage, but it can help with movement. Dark backs absorb sunlight, heat up, and emit that heat back into their environment. That lowers the viscosity of the air or water around the animal and makes it easier to move through. Bellies are light because there’s no need to make pigment for an area that doesn’t get hit by sunlight anyway. This is just one of many effects of countershaded bodies, though, as I wrote about at greater length for this video.
Of course, the true answer, as in so many situations that are popularly presented as “this or that”, the answer is probably both: Countershading helps with camouflage in some cases and helps with other things in other cases. Besides, it can’t have nothing to do with camouflage, because one of the few places where animals aren’t countershaded are snow-covered, where dark backs would stand out. And that’s why arctic foxes, unlike their redder cousins, are adorably monochromatic.