To explain the phenomena that we must learn about complementary colors. Complementary colors are pairs of colors that, when combined or mixed, interrupt each other by producing grayscale colors.
Almost every color in spectrum has its own complementary color, for example, for red it is light blue and blue is yellow. For some reason, the green color is different. It is not entirely understood why but human brain basically invented new color – pink – which is a free color to green. My theory is that nature likes symmetry and human brain created pink to maintain colorless color symmetry.
OK, but why do we look pink if it's a free color to green? Why do we see colors at all?
We see colors of reflected wavelength. Let's take the course, we see it as yellow because almost all visible spectrum is absorbed, expecting yellow light (570nm ̵
In that case, human brains will come up in the system so as not to get confused. If the object reflects red and green, for example, the human brain interprets it as color between them, which is yellow. If it is purple and green than we see blue and so on. Of course, in the case of more wavelengths, it is a bit more complex, but the principle is the same.
There is a specific case when the human brain does something strange, something else. If the object reflects red and purple technically, we should look green, but the human brain decides to see free color for green instead – pink color invented by our brains.