Comment by lodi

> So e.g. when the light is pure orange, it falls down into red wavelength range and is counted as red.

If you only work with one photon at a time, then yes, you don't know if the photon passing through the filter was red, or orange, or with smaller probability even green or blue. But when you have trillions of photons passing through, you can "see" the difference by the relative intensity of light.

Remember that at the quantum level, things don't happen deterministically; you have to consider the probability that a given outcome occurs. So the photon has a certain probability to hit the filter and get absorbed, a certain probability to pass through the entire depth of the filter, a certain probability to hit the sensor without generating an event, a certain probability to hit the sensor and initiate a chemical reaction (for film or biological eyes) or an electron cascade (for CCD sensors), a certain probability to quantum tunnel to the other side of the universe...

So getting back to your question, when pure orange photons hit a red filter, many of them will make it through the filter, but not as many as if they were pure red photons. When pure orange photons hit a green filter, some of them will make it through, but not as many as if they were pure green photons. So if your brain knows what the "white point" of a given environment is, relative to that white color it'll see a specific combination of "some red, some green" as orange. (Of course, if known-to-be-white objects are already orange--like when you put on amber ski googles--your brain will eventually adjust and recalibrate to perceive that color as something else... perception is tricky!)