First, remove the old stuff,
varnish, cetol, whatever. Then apply two coats of varnish. Now, sand and
paint it grey like the color of weathered
teak. The paint will last longer than 12 coats of varnish, and can be touched up, but going back to varnish is possible, because the varnish coats have sealed the timber, and the paint will come off clean with a heat gun, with no seepage into the grain of the
teak. It is a user-kindly strategy for going to the tropics, and saves you heaps of
work. In the long run. Other colors I've seen used have been a kind of golden teak color and a deep maroon. I was surprised how good the maroon looked, but I personally prefer the grey. It can, of course be whatever color you want, even reflective paint so it really shines when the sun or a spotlight strikes it. Makes you really show up in an anchorage.
Ann