Teak varies tremendously in color. Some will be darker, some will be lighter. Could you drop a few pictures in this thread so I can understand the exact shades you are talking about?
Last year, I removed all of the old, nasty varnish
from my teak which was also 20 yrs old and very dark looking. Once I stripped the varnish, the teak gleamed like new. I then oiled mine (with oil
that is colorless) to let the teak's natural color show through. Here are a couple photos. Notice the widely varying colors of my teak. The teak on the bulkhead with the doors is a golden color, while the other teak is not. In my case, it's from 20 years of sunshine bleaching out the more "golden" colored teak. The darker stuff is the natural color in my case.
Also, a more striking example would be to note the handle and framework around the companionway
in the galley photo
. See what a very different and "golden" color it is compared to the rest of the galley's teak. Again, this is due to sunlight bleaching it. All teak on this boat was stripped of the old varnish, sanded smooth and then oiled.
Teak is also a very coarse and grainy wood. There are various spots that are almost black and others that are very dark brown. You won't be able to sand these away, as they are part of the wood. Embrace the natural character of the wood and don't expect an even looking (modern, plasticy) feeling. It is a very diverse wood. I say this from experience. We tried to make it look "modern" and failed. It was a big mistake. We had to go back and re-finish the traditional way for it to look right.