In the nineteenth century some scientists, James Clerk Maxwell being a notable example, had the idea that if you filmed the same scene onto black-and-white light-sensitive transparency (the only sort available at the time), with one camera through a red filter, a second camera through a green filter, and a third through a blue filter, and then projected these films synchronised through their respective colour filters, you’d get a full-colour photographic image. That was a bright idea because so you do, but the technology of the time made this triple-synchronisation tricky and unsatisfactory.
Some found, however, that using just two cameras and two filters, one red and the other green, you still get close to full colour, i.e. you get blue too, just from red and green. This technique was developed by a number of people, notably Claude Friese-Greene in the early decades of the twentieth century, some of the movie films he made using red and green filters can be seen on YouTube, e.g.
London Bridge 1926. Early cinema colour movies, for example those using the Technicolor process, used essentially the same technique, using light splitters rather than two cameras.
In the 1950s Edwin H. Land began to do academic experiments on this phenomenon, as explained in his 1959 paper
Experiments in Color Vision. Land discovered rather by accident that if the green projection filter be removed the resulting image was, though rather washed out, still in full colour. How? How is it that the eye is perceiving full colour, from a projection that is only shades of red and grey? This phenomenon is called colour constancy and has never really been explained. I have a hypothesis as to why, which you can read in the writeup on my page
Equivalent Colour Brightnesses. That is however a theory based upon conjecture, as so many are, though I think has some observational credibility about it.
Examples of colour constancy – quite striking examples – can be see on my pages
Colour Constancy,
Colour Constancy Overlays and
Simulated Colour Filters.
Whatever is going on is obviously of significance when choosing colours for visual presentation, and especially so if that choice is being made mechanically, as increasingly it is likely to be. Relative brightness plays a significant part – that is the brightness of an area in relation to the areas around it, not its absolute brightness so much as that can change with the ambient light, more how it relates to nearby shapes, and the other aspect that has great significance to this is size of an area.
My researches and experiments are primarily around this topic of colour perception in the spiritual sense (as opposed to the mechanical) and of colour constancy and its role in this.