Conform as closely as possible to the lights/shapes required.
Rule 31: Seaplanes
Where it is impracticable for a seaplane or a WIG craft to exhibit lights and shapes of the characteristics or in the positions prescribed in the Rules of this Part, she shall exhibit lights and shapes as closely similar in characteristics and position as is possible.
Wording follows the International Regulations as printed in the US Coast Guard Navigation Rules handbook (2024), with British spelling, and is shortened in places. Download the rules
Read the whole of Rule 31 on one page
Rule 31: Seaplanes
Where it is impracticable for a seaplane or a WIG craft to exhibit lights and shapes of the characteristics or in the positions prescribed in the Rules of this Part, she shall exhibit lights and shapes as closely similar in characteristics and position as is possible.
A training aid, not the official text. The COLREGs are an IMO convention, and your national authority publishes the version that applies in its waters. Check the rules themselves before you rely on them at sea. Download the rules.