Grouped tightly enough, this combination of red and green wavelengths will provide a perception of the color we call “brown”
If you defined “brown,” you’d have to do it that way - by describing the wavelengths that we perceived as that color. The fact that your phone screen - a technology that works by emitting light - can display brown means there’s light that we call “brown.” It may happen that is really a dark orange, in much the same way that pink is a light red, but so what? It’s light and we see it as brown. Brown light.
If you defined “brown,” you’d have to do it that way - by describing the wavelengths that we perceived as that color. The fact that your phone screen - a technology that works by emitting light - can display brown means there’s light that we call “brown.” It may happen that is really a dark orange, in much the same way that pink is a light red, but so what? It’s light and we see it as brown. Brown light.