Opposite gybes downwind
The situation
Both boats run downwind on opposite gybes and their tracks converge. Green has the wind on her starboard side (boom out to port); Red has the wind on her port side.
The question
Does port/starboard still apply when you're sailing downwind?
The ruling
Yes. Rule 10 applies everywhere on the course, not just upwind. Green is on starboard tack and has right of way; Red is on port tack and must keep clear. Tack is set by the side the wind is blowing over — the side opposite the mainsail — regardless of which way the boat is heading.
Port/starboard applies downwind too — your tack is set by the windward side, not your heading.
Opens the situation on the boat-length grid — scrub it and see exactly how the boats meet. Free, no account needed.
Rules cited
See the underlying rule: Rule 10 — On Opposite Tacks (Downwind).