What is the colour of things in the dark?

"'You said that there were two things to say,' said John, 'What was the second?'
'The second was this. Did you think that the things you saw in the dungeon were real: that we really are like that?'
'Of course I did. It is only our skin that hides them.'
'Then I must ask you the same question that I asked the giant. What is the colour of things in the dark?'
'I suppose no color at all.'
'And what of their shape? Have you any notion of it save as what could be seen or touched, or what you could collect from many seeing and touchings?'
'I don't know that I have.'
'Then do you not see how the giant has deceived you?'
'Not quite clearly.'
'He showed you by a trick what our inwards would look like if they were visible. That is, he showed you something that is not, but something that would be if the world were made all other than it is. But in the real world our inwards are invisible. They are not coloured shapes at all, they are feelings. The warmth in your limbs at this moment, the sweetness of your breath as you draw it in, the comfort in your belly because we breakfasted well, and your hunger for the next meal- these are the reality: all the sponges and tubes you saw in the dungeon are the lie.'
'But if I cut a man open I should see them in him.'
'A man cut open is, so far, not a man: and if you did not sew him up speedily you would be seeing not organs, but death. I am not denying that death is ugly: but the giant made you believe that life is ugly.'
'I cannot forget the man with the cancer.'
'What you saw was unreality. The ugly lump was the giant's trick: the reality was pain which has no colour or shape.'
'Is that much better?'
'That depends on the man.'
'I think I begin to see.'
'Is it surprising that things should look strange if you see them as they are not? If you take an organ out of a man's body- or a longing out of the dark part of a man's mind- and give to the one shape and colour, and to the other the self-consciousness, which they never have in reality, would you expect them to be other than monstrous?'
'Is there, then, no truth at all in what I saw under the giant's eyes?'
'Such pictures are useful to physicians.'
'Then I really am clean,' said John. 'I am not- like those.'
Reason smiled, 'There, too,' she said, 'there is truth mixed up with the giant's conjuring tricks. It will do you know harm to remember from time to time the ugly sights inside. You come of a race that cannot afford to be proud.'" C.S. Lewis, The Pilgrim's Regress, Book 4, Chapter III