This is a continuation of my last question in which I showed that color does not exist in reality but only in our perceptions. So I ask, is seeing something which does not exist not classified as hallucinating?
A halluncination is to have a perception in the awake state when there is no external stimulus.
Colour is not a halluncination. Instead, it is the result of our processing of visual stimuli in the mind, see e.g., my answer to the previous question Is color intrinsic to light?
Analogously, hearing tones is the result of our processing of auditive stimuli in the mind.
In both cases, an external stimulus exist and serves as input to the processing.
The Madhyamaka school of philosophy sees all reality as empty of essence, all reality is seen as a form of nirmita or magical illusion.
'Hallucination' is not often seen in Buddhist scholarship, only "illusion" and "dream". These terms have a different significance for different schools. e.g. the appearance only school claim:
It is just as [something] made into a magical illusion with the power of an incantation (mantra) appears as the self of an elephant. A mere appearance (ākāramātra) is there, but the elephant does not exist at all.
While this does not quite meet every definition of 'hallucination', because there is a thing which is made to appear like an elephant (colour), suchness, the "mere appearance" is not created from external sense stimuli, but a construction of an unconscious mind.
And "hallucinations" are often defined as things which occur without an external stimulus; as opposed to "illusions" which are misinterpretations, e.g. thinking the wind is someone crying.
Buddhists are also fond of the term "delusion" for believing in these elephants.
Colour is what we see as a consequence of a brain's interpreting. I think once a light ray of some specific frequency hits the eye, brain interpretes it as some colour. But all the brains do not work alike. Some see the red I see in blue or some other colour. However it doesn't follow that colour is a hallucination. We cannot isolate colour. What a stoner sees is an imaginary joint wrapped in white paper but not "white". White is there as a consequence of his memory. Colours do not exist. Only frequencies of light do. If instead on an apple we saw a number saying x-Hz then we all would see it as it is.
The answer to the question is YES - colour is a hallucination. All our senses are inputs that via biochemical signalling causes mind made creations (useful interpretations). The difference between, say, drug-induced hallucinations and sense perceptions is that these agreed upon hallucinations are what we call reality. It is clear that invisible wavelength variations are not colour (so the red of a rose petal is not a characteristic of the petal but the translation of the wave information into an experience (qualia) we label as red. If an inverted cone is placed between two light sources and casts a shadow at either side - when a cyan filter is placed over one it not only creates a cyan colour shadow at the same side, it creates a RED one on the opposite side. Equipment will detect it as grey (as will visual equipment that zooms in and removes context). This is because the mind calculates that a grey output when there is a cyan context must arise because the complementary colour red is creating the grey shadow. In other words, the red is absolutely mind made (which clearly shows it is capable of such illusions and therefore putting colour where it does not exist in the real world). Colour-blind synesthesia sufferers sometimes see colours that they have never been able to see due to the colour-blindness showing that the sensory organs may have to operate in a normal way to provide the full colour range most people enjoy and this too shows that these are effectively hallucinations (because they are clearly non physical experiences that are mind created). The BIG question is how did the mind create such arbitrary experiences with no out there references???... This has taken a long time to work out (and the answer could relate to where wavefunctions reside in their coherent probabalistic form)
But it does exist! can't you see it? it exists in your mind!
The neuroscientist Rodolfo Llinás once put it colorfully, saying that "Life is nothing but a dream guided by the senses."
Also, out of my sleeve, prima facie it seems easy to distinguish hallucinations from colors by examples.
For example, that color is a means of representation of reality and hallucination is the content of such representation.
For example, you hallucinate that an apple is blue, by means of the experience of the color blue.
Color is real just as you can count five fingers. Your brain is reporting frequencies an those are perceived as colors such as tonality of sound. You can't consciously count the vibrations of particles but you can recognize a song. There's a difference between the abstract idea of something and the subject in reality. Like the names we give to colors, red, yellow, etc... Those are not intended as a definition of reality but as a communication tool, known as language.
I would say that our experience of color is constructed within subjective reality. Whether we call that construction "accurate" or "a hallucination" simply depends on whether we believe that construction corresponds to something in objective reality (e.g. photons of particular wavelengths). (If we're not awake, we wouldn't call a non-corresponding construction a hallucination, we'd just call it a dream.)
Here's a short video that you might find interesting that explores this kind of discussion further: