What does it mean that color a “visual phenomenon”? Does color not exist outside of our brains?
Different wavelengths of light are absolutely a real, physical thing, but the *interpretation* of those wavelengths as specific colors is entirely due to how your brain interprets light of different wavelengths.
What is fundamental to your question that no-one has mentioned is the concept of qualia.
Essentially, everything you ever experience occurs within the confines of your body. Your understanding of reality is a sensorium created by your brain. It reflects reality, but it isn’t accurately representative of reality. We can never truly experience light, we can only imperfectly sense it with our imperfect senses.
Basically, color you see is the same to ~~electromagnetic~~ visible light spectrum what greens and oranges are to terrain elevation on a map. Mountains aren’t really orange, it’s just a way of indicating higher elevation by agreed means. And in analogous way, color is what our brains decided to represent differences in absorption of visible light.
To add to the complexity, we’ve evolved to have retinal cells that can discern certain wave lengths clearly and interpolate others. So if something is red our red receptors see it clearly, but if it is orange, or magenta, our red and blue and green receptors each see it imperfectly, and our brain pools their inputs, and figures out it is orange, or magenta
The only difference between red light, green light, and blue light, is the wavelength at which the photon is oscillating. The physical effect of color is a product of our brain, and how we perceive this differences in wavelength. This is no different that the way your radio interprets different radio waves to make different sounds, yet fundamentally they are all the same.