Possible Clues:

• As a rule, tuna is cooked and served without dressing
• Uncooked tuna - a rule that's variable
• Plain gold's oddly neutral
• A rule aunt adopted about appearing in the nude
• Dad's sister tours a river and lake with nothing on
• Cooked plainly or raw
• Sauna bath cures — all stripped naked
• Uncovered
• Naked relative admitting a rule's broken
• Uncooked tuna -- a rule that's broken