How can I remove brown coloring/stains from logs?
Had a similar problem with building a 10" round log home, some of the logs got wet. We tried everything including sandblasting to remove it. 

The only solution we found was 40 grit sandpaper on a random orbital sander to really rough it up and remove 1/16" to 1/32" of wood before we switched to 120 and 200 grit to smooth it back out. Matching the stain might be tough though.