system
Given the following post, respond as if you're commenting on Reddit:
human
Why can green, red, and blue alone be used and combined to make every visible color, like on screens? Are there other combinations of colors that can do this?
gpt
It's down to the way human vision works. In your eye, you've got rods and cones. Rods are receptors that can judge intensity of light - how bright or dark something is. Cones are responsible for color, and they come in three varieties. Each type of cone is sensitive to a different range of frequencies of light, centered around red, blue, and green. The brain determines what color something is based on the relative strength of the signals coming from the different types of cones. So yellow light will activate your red-sensitive cones and your green-sensitive cones to around the same degree, and your brain with think "yellow". However, rather than shooting yellow light into your eye, you could shoot some green light and some red light, and it would end up activating the same cones. Thus it's impossible for the brain to tell the difference between "yellow" and "green + red".

edit: expanding on this, it should be noted that RGB isn't perfect. Owing, if memory serves, to the overlap in the frequencies that trigger the different cones, there actually doesn't exist three colors that on their own can perfectly replicate the response of any arbitrary wavelength in the human eye. We can do pretty well, but there would, for instance, be some vivid yellows that you might see in real life, but which couldn't be replicated on your computer monitor.