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if youre talking about the biochemical process behind it in a nutshell there are three distinct molecules that change shape in your retinas cells when light of their respective color hits them (they are red, green and blue). mixed colors like yellow stimulate multiple types of molecules to a lesser degree and this is how your brain "knows" which color this EM frequency resembles.
if youre talking about your perception of this process youre really entering the realm of philosophy because the question "is your red the same as my red" is closely linked with consciousness and peoples experience of their own life. if you believe that emotions (fear, love, anger) and especially sensory stimuli (pain, heat, cold) feel the exact same to every human or even conscious being than it seems reasonable to assume the same is true for qualia like colors or sounds.
