To expand on Prof Ng's comment on color perception, it reminded me of qualia https://en.wikipedia.org/wiki/Qualia. It describes how instances of subjective experiences, and one of the most well known examples is whether the "redness" of red that you see is the same as the "redness" of what someone else sees. There's biological basis that that our eyes respond to red in the same way but it's difficult to answer whether the subjective experience is also the same