Our idea of "warm" colors is just a historical accident. Wood burns orange because it produces soot, which glows orange in the flame. Same applies to candles too, because there’s never enough oxygen to burn all the carbon.
If we’d started with purified hydrocarbons instead, blue might have been the ultimate "warm" color. Natural gas burns with a blue or even invisible flame, a sign of complete combustion. Orange, then, would be the color of flawed, struggling fire.
Imagine a house heated and lit by a gas furnace instead of a traditional fireplace. The light from the fire would be blue, and we’d associate that glow with warmth and coziness. Picture old paintings with a cozy atmosphere, their hearths glowing blue. If everyone grew up like that, blue would be the warmest color instead of orange.
"Different flame types of a Bunsen burner depend on oxygen supply. On the left a rich fuel with no premixed oxygen produces a yellow sooty diffusion flame; on the right a lean fully oxygen premixed flame produces no soot and the flame color is produced by molecular radicals, especially CH and C2 band emission."
Source: Wikipedia
Oh that is a good point. The sun really is pretty orange. Long before the first fire, people probably associated orange and yellow with warmth.
However, cultural associations can change over time. What we consider warm is largely sustained by old paintings and pictures. Modern day artists use orange to convey a warm atmosphere, and that's why the idea of orange as a warm color persists.
People don't really use fire that much any more, so realistically speaking, warmth doesn't even have a color today.
I'm going to add to the sun point, and remark that the cool range of tones is associated with snow and ice, since these reflect the blue of the sky. So even if people didn't need fire to cook or live their lives at all, they would associate the blue ranges with winter.
Water in its liquid state also looks blue, and is usually associated with something refreshing in warm areas. So even in the tropics you would have a reason for associating blues with cools.
In contrast, most desert areas are naturally in orange ranges. You can also argue autumn forests would look orange and they're not exactly warm, but the light in an autumn forest doesn't bounce as much or as tinged compared to light conditions in desert areas, where the soil or sand is yellow or orange -red, and where whatever casting a shadow is probably the ground itself.
Finally, human bodies are more in a warm range tone (no matter the skin color) when compared to the same body suffering cold. Nails and lips take on a bluish hue, so do fingertips.
I think you would need to tweak your universe a little bit more to achieve a reversal in color association.
Those are some pretty solid points! Especially the one about healthy vs. freezing skin tone.
Those substances are blue due to Rayleigh scattering, not because they reflect the sky
The highest energy (shortest) wavelengths scatter first, so out of visible light blue is the first scattered colour
People use fire to cook with all around the world several times a day.
Not forgetting people who have fires and stoves etc too warm their homes and that.
What are you on about?
Developed countries with electricity and district heating. What you're saying still applies to the rest of the world though.
The sun is white at mid day
Ok, so white should be the warmest color if you just stick with natural and easy to observe examples. Sunrise can be pretty nice and warm after a cold night though, so in a narrower sense red/orange/yellow could still be considered warm. However, during sunset, it gets cooler again, so the same colors would be cold compared to midday white. It gets a bit messy.
The sun is, by definition, white. White is what we call it when an object reflects all spectra of sunlight.
It's only at sunrise / sunset when the atmosphere filters out more of the blue spectrum that it apparently turns more orange/red.
White light is light that contains all visible wavelengths at the roughly the same proportions. The sun has nothing to do with this definition.
Our sun is actually slightly greenish-blue as that is where it's peak (visible) output is.
The key word there is "visible". Our eyes adapted to the spectra of our star when filtered by our atmosphere. We perceive that spectra as white.
Our perception is limited and our understanding has long outgrown it. White light, by definition is all visible light at equal intensity, thus the sun is NOT white.
Use RGB codes for example. White, by definition would be 255, 255, 255.
The Sun is more like 245, 253, 255 or something .... still looks white enough to us, but by definition, isn't.
Can we agree it's not orange? That is what I was originally pointing out.
From a physical standpoint, sure.
But I'm pretty sure that if you casually ask most people which colour the sun is, you'll hear yellow/orange much more often than white. So for the context of which colour was, prehistorically, associated with warmth I think yellow/orange are the more relevant answers.
Actually...
our eyes adapted way back when our ancestors were fish. So we see light in the range that light passes best under water.