Teak is a very oily wood with lots of variation in color from tree to tree. As you are finding out!!! After exposure to moisture, UV rays etc... It can and will change colors. If left untreated it will usually turn to a Gray color. You can use Laquer thinner or Acetone to clean the wood some times to "Lighten" it a bit and there are some commercial "Bleach" type cleaners for it but part of the beauty of this wood IS it's color variances. Since you have sealed it you are pretty much stuck with what you have now. Of course you could be a "Dumb OKIE" and Paint it!!!!!

BUT.... If you do, I will be forced to drive ALL the way back east and Kick your Yankee Butt!!!!!!!!
P.S. I think it looks AWESOME!!!!!!