The brown stains are tannic acid, the same natural stuff in the teak that is in coffee beans and tea leaves, which is why they make hot water turn brown.
Depending on where the scratch is, remember that the panel of the door is plywood, not solid teak. Sanding is very touchy, as the teak overlay is probably no more that 1/32" and maybe less.
I agree with the comments about what Marinette used originally, I'm as sure as I can be that natural teak was just oiled. As the wood and the finishes have aged, the "honey" color has increased, just like old hardwood floors are darker than new hardwood floors of the same wood species.
I suggest getting a furniture repair expert over there if it's a major scratch that you cannot handle on your own. These guys can absolutely make disasters disappear. The downside is that now and forever you will have a man made section of the door that cannot be just oiled like the surrounding areas.
I made up my own mix of teak refinisher last year and have redone all of the interior teak. A little patience, very little elbow grease and the interior looks like new. My tools were rubber gloves, a few throwaway natural bristle brushes and a few pads of bronze wool. After amalgamating the old finish (dissolve and spread around), I did a standard application of new teak oil.
I'll look to one of the gurus to help me here: I still have never managed to get a photo onto the site. Someone offered a while back to get my photos on the site if I would email them to him. If the offer still stands, let me know. I have 6 before and after shots of my teak that I hope will impress everyone. I have the recipe for my chemical brew, I can make more a send it to anyone who wants to try it. I intend to package and trademark it "one of these days"...
JIM
Alexandria, VA
1989 32' Sedan
'Gammelby'
Friendship, MD