Just to bring this to closure. I sanded some more and more and more. I tried the oxalic acid and letting it sit in the sun. Nothing changed the appearance of the teak, so I decided it is a 20 year old boat and it should look like a 20 year old boat and I will just Cetol it and it is what it is.
So I applied 3 coats of Cetol Natural and 2 coats of Cetol gloss and I am almost ready to remove the masking tape. Here are the results for the toe rail:
and the rub rail:
The stripes never went away, but I did notice that they shift their appearance when viewed from different directions. Looking aft some areas look light and dark, looking forward the same areas look dark and light.
I was in a furniture store over the weekend and a fella was buying a nice looking bedroom cabinet set of drawers. He said he liked it because it was Tiger Maple (it had the same stripes in the wood). I asked him what that was and he said it is from the heart of the tree, it has these tiger strips in it and looks special. So maybe I am dealing with "Tiger Teak" and maybe not. But I think it looks just fine.