# Is anything coloured “infra-red”?

All our day-to-day objects are things we can see, and thus we can conclude that their colour lies in the visual spectrum. Is there matter that does not have a colour within the visual spectrum? What am I not understanding correctly?

• "and thus we can conclude that their colour lies in the visual spectrum" -- not if they are black in the visible spectrum, which means they don't reflect any appreciable amounts of light on the visible spectrum. Likewise for transparent things, as in Ruslan's answer. – Hypnosifl Nov 8 '14 at 0:14

You surely know that glass is colorless in visible spectrum. But it does absorb in IR and UV parts of spectrum. Here's a sample spectrum of borosilicate glass 3.3, universally called Pyrex glass:

source

If our eyes could see light with wavelengths around $3\,\mu\text m$, we'd actually see this glass sample as coloured, but, as you can see, the whole visible range of $400\,\text{nm}-700\,\text{nm}$ is almost fully transmitted ($92\%$ transparency), and this is all we can see, so we say it's transparent.

All our day-to-day objects are things we can see, and thus we can conclude that their colour lies in the visual spectrum.

Because we see only in the visible spectrum, an object's colour is a consequence of how it interacts with that region of the spectrum. All colour lies in the visible spectrum. This is just what colour is.

Is there matter that does not have a colour within the visual spectrum?

Matter does interact with other regions of the spectrum, but those regions are not interpreted by our eyes and are not considered to be "coloured". We can use equipment that takes infrared photographs and maps those wavelengths to others that we can see. This allows us to see differences in that region that were previously invisible.

Other creatures that could see in the infrared region might well describe them as having different colours. Humans wouldn't do so. All we can do is say they have differing IR spectra.

It may be possible for the Human eye to see a little way into the infra-red by replacing Vitamin A in the diet with A2.

The frequency distribution of radiation emitted by a body is determined by its temperature in accordance with Planck's law (http://en.wikipedia.org/wiki/Planck's_law). e.g. http://upload.wikimedia.org/math/2/8/1/2812991818a5f62e981118a582e433bd.png.

Any object at a finite temperature will emit some radiation in the infra-red region of the spectrum. If we detect that infra-red radiation e.g. with an infra-red camera which converts the infra red radiation detected to visible light on the screen we can see" the object using its infra-red radiation. Unfortunately our eyes do not work in the infra-red region of the spectrum, so we cannot see infra-red emitting objects directly with our eyes.

It interesting that some flowers do have invisible patterns to us. These patterns can be seen only in ultraviolet frequencies that bees can see. I don't know if there is an equivalent case for infrared in biology.