Don't use oil on the deck. All it does is attract and hold dirt and wii tun blackish eventually. The only way to get the color back on a teak deck is to remove the upper layer of wood cells that have turned gray. There are two ways to do this--- sandpaper and teak "restorers." Both of them remove wood--- the sandpaper does it physically and the teak restorers do it chemically. And wood that goes away you can't get back. So if you want to shorten the life of your teak deck sanding or using restorers is a sure way to do it.
There is only one "best" care for a teak deck and that is to wash it periodially with salt water and a detergent like Joy. The reason most of us use Joy is because it suds up really well in cold water. The reason you use salt water is because if any water can get down through separated seams under the decking or migrate down alongside deck screws and into the wood core of the subdeck, salt water is much less condusive to promoting rot that fresh water. If you boat in fresh water you can make your own salt water to wash the decks with---- the wood won't know the difference.
We use a regular old string mop to wash our decks. This doesn't have any detrimental effect on the wood. A few times a year we give it a bit more of a scrubbing using the same salt water-Joy mixture and a 3M Doodlebug. BUT---- we go over the wood very lightly with the Doodlebug and we always go across the grain unless deck hardware prevents it.
The reason to ALWAYS go across the grain is that teak is made up of runs of soft cells and hard cells. If you go with the grain with anything abrasive--- Doodlebug, coarse pad, etc--- it will "dig out" the runs of softer cells. While not noticeable at first, over time these tiny linear grooves will become deeper and the softer cells will continue to weather out faster than the harder cells. If you make a practice of scrubbing the deck with the grain, these little grooves will become crevices will become canyons. Cleaning across the grain minimizes the damage you will do to the softer cells.
And for the same reason, never, ever, EVER powerwash a teak deck. I dont care how many people tell you they powerwash their teak decks with no detrimental effect, they're dead wrong. They just don't know it. Even a light setting on a powerwasher can be enough to hydraulically "mine" those uppper layer of soft cells away and you have set the stage for the eventual crevicing of the wood.
If you have a problem with algae growing on the deck in the winter like we can have up here, washing the deck with a mixture of vinegar and water will help keep it at bay.
But if yiou want a brown deck, you've got the wrong material because anything you do to keep it brown will remove the upper layers of wood cells and the deck planks will be that much thinner.
Years ago we priced the cost of having our main deck replaced. At that time--- 1999 or so--- the estimates ran between $20,000 and $30,000 depending on who we got the bid from. Since then the price of good quality teak has gone through the roof and of course labor costs have gone way up. But that was a real motivator for us to learn everything we could about the proper care of a teak deck so we could extend the life of our now-39 year old deck as far out into the future as possible.
A teak restorer example---- Awhile back I was associated with a 120' corporate yacht. The steel Phillip Rhodes-designed yacht was built in 1966 and had teak decks inside and out. Because of the way the yacht was used it was imperative that the decks look like new teak year round. Which meant the crew made liberal use of chemical teak restorers on the exterior decking. The life of the teak decking was shortened considerably--- it had to be replaced every eight or ten years---- but the staggering cost of doing this was figured into the operating budget of the yacht. The company owned the yacht for several decades and during that time all the main decking was replaced several times.
I did not learn all this myself through years of being a shipwright or anything like that. I learned it from several people who are or were very experienced shipwrights with specialties in deck work as well as a couple of excellent books on the care and feeding of wood on a boat.
Bottom line--- learn to love silver-gray, don't sand it, don't chemically restore it, don't oil it, just keep it clean with soap and water. And it would be a good idea to learn how to repair deck seams that pull away from one side or the other of the groove because this is how moisture gets down under the planks where it can promote rot in your subdeck. If that happens then you can be looking at a really BIG bill. Or a really big job if you elect to fix the problem yourself.