'They're red when they're boiled, and blue when they aren't.

If you mixed live and dead lobsters you'd get Tyrian purple.' '_I_ shouldn't like to mix anything with a live lobster,' said Anthea, shuddering.
'Well, there aren't any other red and blue fish,' said Jane; 'you'd have to.' 'I'd rather not have the purple,' said Anthea.
'The Tyrian purple wasn't that colour when it came out of the fish, nor yet afterwards, it wasn't,' said Robert; 'it was scarlet really, and Roman Emperors wore it.

And it wasn't any nice colour while the fish had it.

It was a yellowish-white liquid of a creamy consistency.' 'How do you know ?' asked Cyril.
'I read it,' said Robert, with the meek pride of superior knowledge.
'Where ?' asked Cyril.
'In print,' said Robert, still more proudly meek.
'You think everything's true if it's printed,' said Cyril, naturally annoyed, 'but it isn't.

Father said so.