Possible Clues:

• Turning brown — Russian river, as is to be expected
• Normal, like Cumberland's son?
• A certain success is not affected …
• Unaffected by this gas
• Illegitimate in respect of birth, receiving query regularly
• Unaffected; colour
• Note name, around time of hearing
• Obvious choice for bicentenarian as to the 1 down of 5 across
• Tenor breaks into note heard neither sharp nor flat
• Simpleton, one short of being sharp?