What determines colour?

[saor]

So let's say I've got two pieces of plastic on my desk - one red piece & the other blue. Light hits the two pieces and the respective wavelengths of light are reflected/absorbed and I end up perceiving either red or blue. Ok so pigment is added to plastic to colour it - fine. But what is it about the pigment that makes it reflect/absorb certain wavelengths of light so that we end up receiving & perceiving those wavelengths that correspond to red or blue?

Or to re-phrase it: If we were to view the molecular & atomic make-up of those two pieces of plastic in the absence of white light but under different conditions like UV - what would a person look for that would allow you to say: "Ah - see that? That property right there tells us that under normal lighting conditions the objects' colour will be perceived as red or blue."

This is for anything (oranges, paint, flowers etc) - not just plastic pigment .

Also I've heard a few times the question: "Is an orange still the colour orange in the dark?". And to avoid a semantic mess I'll preface by saying that I'm ok with either definition of colour for the sake of this question:

a.) Whether you define colour as the eventual wavelength that we perceive after it's having interacted with the orange (and thus the orange isn't orange in the dark) or,
b.) You define colour as that property or propensity of the orange to reflect (under normal lighting conditions) that particular wavelength of light which we end up perceiving as orange. Which is a bit messy because then the definition of 'colour' is dependent on 'normal' lighting conditions, but it still means the orange has those properties even in the absence of 'normal lighting conditions'.

Damn pls don't get into semantics . I'm just curious about that property of things which results in certain wavelengths of light reaching our retina.

 

[LazyLion]

Eddies in the space time continuum.

 

[Messugga]

So let's say I've got two pieces of plastic on my desk - one red piece & the other blue. Light hits the two pieces and the respective wavelengths of light are reflected/absorbed and I end up perceiving either red or blue. Ok so pigment is added to plastic to colour it - fine. But what is it about the pigment that makes it reflect/absorb certain wavelengths of light so that we end up receiving & perceiving those wavelengths that correspond to red or blue?

Or to re-phrase it: If we were to view the molecular & atomic make-up of those two pieces of plastic in the absence of white light but under different conditions like UV - what would a person look for that would allow you to say: "Ah - see that? That property right there tells us that under normal lighting conditions the objects' colour will be perceived as red or blue."

This is for anything (oranges, paint, flowers etc) - not just plastic pigment .

Also I've heard a few times the question: "Is an orange still the colour orange in the dark?". And to avoid a semantic mess I'll preface by saying that I'm ok with either definition of colour for the sake of this question:

a.) Whether you define colour as the eventual wavelength that we perceive after it's having interacted with the orange (and thus the orange isn't orange in the dark) or,
b.) You define colour as that property or propensity of the orange to reflect (under normal lighting conditions) that particular wavelength of light which we end up perceiving as orange. Which is a bit messy because then the definition of 'colour' is dependent on 'normal' lighting conditions, but it still means the orange has those properties even in the absence of 'normal lighting conditions'.

Damn pls don't get into semantics . I'm just curious about that property of things which results in certain wavelengths of light reaching our retina.

Short answer is chemical composition. I think your view of how light is "reflected" by surfaces is perhaps a bit simplistic.

Photons are emitted when an electron drops from a higher energy orbit to a lower orbit. These orbits are a characteristic of atoms and the distance between these orbits - the distance higher-than-normal energy electrons fall, is proportional to the frequency of the light produced.
As light has a constant velocity and V = wavelength X frequency, higher frequency means shorter wavelength and vice versa. This determines the colour of the light you see.

 

[nightjar]

.....definition of colour for the sake of this question:

........ certain wavelengths of light reaching our retina.

The key issue is that 92% of males perceive light and colours in the same way and all have the same concept of red, blue, green etc under normal conditions.

The other 8% are (mostly) red/green colour blind because the cones in their retinas have a genetic defect carried and passed on by females. A tiny percentage, which includes me, is totally colour blind and sees things in terms of contrast. I watched the first 15 minutes of last night's rugby but then gave up because the team jerseys were too similar.

The dynamics are totally skewed when narrow wavelengths are use to examine subjects for specific reasons like microscope stain or documents under UV.

A case in point is the attached photo taken on infra red film.
The subject was an expert seamstress and made the dress herself but she later burnt the diamond shaped panel with an iron and replaced it with spare (same batch) of fabric and a matching colour thread with a visually perfect result. Only my use of infra red film was able to highlight the difference in the thread.