Possible Clues:

• It seems to me to be the old way of saying it
• Seems to be that for writing they're based on spirit
• I gather material for writer getting in the spirit
• Caging the wild animals, I reckon
• I consider it's ink in it that makes this spirit blue
• It seems to me the old way of saying it
• Spirit contains coloured liquid, I suppose
• 'I believe...'
• I'd say unpalatable alcohol contains some black liquid
• Alcohol restricts the source of one's writing, according to author