Natural grey is the best route as noted above. If you want it to have more of a brownish color use a Semco teak sealer. Do not varnish or oil it. Just do a web search on Semco teak sealer. This is the product of choice for decks, fishing cockpit coamings, etc. Me, I have teak decks (but not swim platform) and let them go gray, washing occasionally with a soft brush and clean salt water, or sudsy ammonia for stains. About every two or three years, I use a more aggressive product like Semco's cleaner or Snappy Teak Nu.