Some colours may be harmonious when they are displayed together and some may not. The human eye can perceive harmony or disharmony right away as it is a natural instinctive response. We don’t have to think about it to judge it. I haven’t researched on the origin of this response but, even if it is cultural, it has been so conditioned that it has become natural.
It seems that harmony is related to the notion of order and disharmony to disorder. So colours that are harmonious must belong to a scheme. And if they are too different from a scheme, they would be seen as disharmonious.
“Many facets, like a diamond. A diamond that nobody can see as a whole. Some will see one facet, others a second facet but will be blind to the first one that his neighbour can see. I meet you and one of my sides is shining more. Some see only the defects, others see only the purity of the stone. I’m each and every side, I’m the purity and the defect, I’m an outside brilliance and a hidden mystery… Some facets are like mirrors and you think you know me while you only see you own reflection…
I’d like to meet somebody who knows the secret of unity, whose eyes can see beyond what they grasp at first sight. Somebody who will know and understand I can be one thing and another at the same time, one thing and its opposite on the same moment… somebody who won’t be scared away by the dark defect he guesses through a thinner part of me, who won’t be blinded by the most sparkling ideas he guesses beneath the surface. Somebody who will be wise enough to let me show what I want to hide, who will be able to witness the alchemy working on me, from darkness to the purest clarity. Wise enough to let oblivion settles on outdated memories of who I used to be.
A dream of a constant rebirthing day after day, an unseen mutation into an unknown state of mind… no change is death… one track mind is vicious circle… I feel the infinity of life through my soul and through my body, and I cannot but let it display all the varieties of its crystallized energy.”
If you think that Photoshop has changed everything, maybe you need to be introduced to the masters of the darkroom. Before the digital era, skilled photographers did dodge and burn like we do it now digitally, they did combine several negative plates in order to make a new photograph, they did airbrush, literally, to paint or ink over retouched areas, they did mask, they did erase unwanted objects or shapes, they scratched, they painted and drew over the photographs to add details to overexposed areas for example. Photo manipulation does exist nearly since the invention of photography, earlier examples being from the Victorian era. Spirit photography, fantastic creepy photography, people with their heads off, were all the rage back then. Then surrealists and the dada movement used photomanipulation a lot. Propaganda used it a lot too and some dictators erased people they didn’t like from the pictures for example. Then advertising and fashion photography needed this art from the early stage.