Sober today.
Not being an expert in science I can explain it only as best I know how. Light is basically electromagnetic radiation. And like (I think) all radiation, the electromagnetic variety comes in various wavelengths. When the wavelength is within what I believe is a very narrow range our eyes absorb it and spew it into our little chicken heads as light.
Depending on the wavelength the radiation travels at, various colors result. And certain objects reflect and absorb different wavelengths of color. A red sheet of paper absorbs all radiation but the specific set of wavelengths that represent red. A white sheet of paper reflects all wavelengths. Etc, etc.
But as far as I understand it the absorption and interpretation of this radiation of this radiation by our eyes is a purely subjective and evolutionary thing. Meaning that what you think is red isn't actually red, it's just the human brain's way of construing X wavelength. The eye is just a very complex machine that does its job a certain way. But on another planet red might be seen as purple. Or no color at all that we can recognize. Which of course is another reason why science fiction in general is bullshit.
In fact the spectrum in general, the set of wavelengths we see as "light" are again totally subjective. We can't see any electromagnetic radiation outside of that little area, meaning that what you think is dark and light isn't actually dark and light, it's just what you see as dark and light. I believe that most objects that give off "light" -- stars particularly -- also give off many other wavelengths of light that we just can't see. A planet totally dark to us might be totally bright to an alien. Another species that saw in an entirely different set of wavelengths might perceive our entire planet as nothing but blackness but see all sorts of vibrant colors in the deepest oceans of the earth. Etc etc. In fact some species might not see in electromagnetic radiation at all, but some other form of radiation. I don't know much more than that and at this point I'm just going in assumptions.
But there you go. Amazing what happens when you let the drugs wear off.