I, 3. Lichtenberg says that very few people have ever seen pure white. So do most people use the word wrong, then? And how did he learn the correct use? – He constructed an ideal use from the ordinary one. And that is not to say a better one, but one that has been refined along certain lines and in the process something has been carried to extremes.

I, 26. We would say, perhaps, of a green pane: it colours the things behind it green, above all the white behind it.

I, 72. One thing was irrefutably clear to Goethe: no lightness can come out of darkness – just as more and more shadows do not produce light. – This could be expressed as follows: we may call lilac a reddish-whitish-blue or brown a blackish-reddish-yellow but we cannot call a white a yellowish-reddish-greenish-blue, or the like. And that is something that experiments with the spectrum can neither confirm nor refute. It would, however, also be wrong to say, “Just look at the colours in nature and you will see that it is so.” For looking does not teach us anything about the concepts of colours.

I, 81. Can one describe to a blind person what it’s like for someone to see? –Certainly. The blind learn a great deal about the difference between the blind and the sighted. But the question was badly put; as though seeing were an activity and there were a description of it.

III, 102. When we’re asked “What do ‘red,’ ‘blue,’ ‘black,’ ‘white,’ mean?” we can, of course, immediately point to things which have these colours—but that’s all we can do: our ability to explain their meaning goes no further.

from Remarks on Colour, Wittgenstein