does "call white black" here only mean ‘It’s the lucus a non lucendo principle.’ ‘That explains everything. I wonder where we sit.’ A single electric lantern, mass-produced in an antique pattern, had been turned on. The bulb was of that limited wattage which is peculiar to hotels. It did little to penetrate the shadows. ‘The lucus a non lucendo principle is the principle of calling white black.’ ‘Not at all,’ said a voice from the darkness. ‘On the contrary. The word “black” comes from an ancient root which means “to bleach”.’ Q： does "call white black" here only mean "call white black" or also mean "call black white"？ what's the meaning of the last sentence "The word “black” comes from an ancient root which means “to bleach”"?