I use eight coats of clear marine varnish with no color on the outside teak. Now I just light sand it and one coat of the same varnish every year.

Jim;
 I've used the Semco product (on an antique boat I keep) for a few years, then changed to Cetol and then to multiple coats of Bristol Varnish. For me, when applied according to directions, they all worked about the same - give or take a year. But the one thing I did find over the years, is that preparation seems to be more the key - than the final coating. 
Two suggestions I would make. One; Get your teak as smooth as you can by fine sanding with.220 or better. The smoother & cleaner you can make the surface, the better.

Next; Bleach the teak. Use oxclic acid (usually found in teak cleaners) or just regular household  bleach. .This is done not to lighten the teak but to kill the natural bacteria found in the oils of the teak. It is these bacterial that will grow in the natural oils of the teak (even after coated) and produced dark spots. There are plenty of good articles on the 'net' discussing teak prep. 

As to color, it's really more up to you. Test a few pieces on other teak of the same age and make a choice. Teak naturally darkens as it ages because of the oxidation of the natural oils.  Usually, it's more the desired finish (i.e. Gloss, satin, etc.) that is the issue. 
Finally, anything you can do to keep the sun and it associated UV rays off your teak will add a few years to you teak job. Sun covers are easy to make and a worth while project.
Fair winds,
 Bill Dolan
Punta Gorda, FL
#1041 1990-C-36, M-35, WK, Std. Rig, Oberdorfer Mod.