In reply to GFoz:
Physicist top-trumps philosopher any day. You can compare my "red" with your "red". There isn't (yet[0]) much point trying to compare the internal states of my neural net and your neural net, but it is easy to consider the eye as a null instrument and study the conditions under which two stimuli are indistinguishable. It turns out that, for almost everyone, (any) three lamps are sufficient to create a unique sensation of colour - that is, given 3 lamps, one person can create an arbitrary colour and given three identical lamps a second person can match that colour. There are a couple of exceptions; to match a full colour gamut (particularly certain purples) you may need negative chromaticity components, and things get a bit messed up for colour blind people (either with a low sensitivity to certain colours or dichromatic[1]) or tetrachromats[2]. See Feynman(1963), Lectures on Physics, I, Ch. 35-36 for a very readable overview of the subject.
[0] Give it a couple of decades and development of high-sensitivity SQUIDs[3] will mean that ontological subjectivity will have about as big a place in philosophy and neuroscience as God does in understanding the creation of the universe. IMNAAHO.
[1] Only two colour pigments in the eye. Any spectral distribution can be matched by two primary colours.
[2] Rare genetic mutation, theoretically possible only in females. Any spectral distribution can be uniquely matched by
four primary colours. This leads to hugely improved chromatic discrimination. A recent research program is thought to have discovered a small number of tetrachromats.
[3] Superconducting Quantum Inteference Devices. They can already distinguish between emotions and certain primitive thoughts.