Our TVs only produce three different colors: red, green, and blue. With these three colors, our TVs are able to reproduce the sensation of any color we are capable of sensing. This little economical trick is made possible not because of the inherent properties of light, but because of the inherent properties of our eyes. In other words primary colors have nothing to do with the physics of light, but everything to do the eyes and the brain.
Our eyes have four different types of light-sensitive cells. One type of cell, commonly called a rod, is very sensitive to visible light but can only distinguish varying levels of intensity. Three other types, the cones, require higher levels of light, but they allow us to distinguish different colors because each type of cone is sensitive to a different range of frequencies. One type of cone is most sensitive around the red range, another is sensitive near green, and a third near blue. There is overlap. Both the red cones and the green cones are stimulated by spectral yellow. This allows our devices to fool our eyes and minds into seeing yellow by mixing red light and green light. From a physics standpoint, red and green mixed is not the same as yellow, but we cannot distinguish these two cases. The graph below shows the approximate range of sensitivity for each of the three types of cone cells.
Primary colors come in two types as shown in the image below. Mixing light has an additive effect (shown on the left) while mixing pigments has a subtractive effect (shown on the right).
Because TVs mix light, this effect is additive (i.e. red and green make yellow, red and blue make magenta, and blue and green make cyan). To make white we mix all three primary colors (red, green, and blue) at their full intensity. Mixing them evenly at lower intensity levels produces gray while black is merely no light at all. White from the TV has a fundamentally different quality compared with white from the sun. White from the sun contains all frequencies while white from the TV only has red, green, and blue, but these whites still look the same to our eyes.
Mixing pigments takes away light. Each pigment absorbs different frequencies so mixing them together combines these effects. Magenta pigment absorbs green light and yellow absorbs blue light. When these pigments are mixed, all but the red light are absorbed. Magenta, yellow, and cyan are the three primary pigment colors used by modern printers. There are many possible primary color schemes for pigment, but the magenta-yellow-cyan scheme works better than the red-yellow-blue scheme most of us learned in grade-school art class. Artists know very well that you cannot mix every possible color with only red, yellow, blue, black, and white paint. This is why oil paints come in so many different colors.
Once again, the reason mixing colors works, whether light or pigment, is because of the way our eyes work. Our intelligent alien visitors may have eyes that work differently. They might have a wider or narrower range of frequencies they can see. They might see infrared or ultraviolet, or they might not even see the red or violet that we see. They might only distinguish intensity, or they may have greater or lesser color acuity because they have more or fewer light sensitive cells analogous to our cones. For example, if they had four cones, they might need a primary color scheme of four colors to display all the colors they can perceive. There is no guarantee that they will look at our TVs and at the corresponding natural scene and perceive them as the same scene.
Besides color, there are other considerations as well. We view TV at 30 frames per second and movies at 24 frames per second. This works with the frame rate and persistence of vision characteristic of our brains to create the illusion of smooth motions. Our alien visitors' brains may have a faster frame rate and they might see the flicker in our devices, which could be so distracting to them that they do not see or enjoy the action the way we do. All this would also be true of our visitors' technological devices. Their devices would be tuned to their brains and we might not perceive the output of their devices at all they way the aliens perceive it.
So whose version of reality would be more correct? Both and neither. Both we and our alien visitors evolved perception mechanisms suitable to our respective worlds which enabled us to survive and develop a technological society. In a practical sense, perception is reality, just as in politics. At the same time, it is not possible for either of our perception mechanisms to completely represent the real world. That would be too much information to process. Instead, evolution gives us just enough to survive better than the alternative while working within practical limits.
Comparing ourselves with a hypothetical alien species is an exercise in imagining whether things are as they must be, or only as they happen to be in our particular case. This is just another way of moving us further from the position we once occupied at the center of the universe before Copernicus and Galileo removed us from that spot more than 400 years ago.
