Welcome to Rehab! I recently rehabbed a bag like yours, but British Tan - bag twins! You've already received a lot of really good advice, just thought I'd add my two cents worth...
Check out this link:
http://forum.purseblog.com/coach/coach-rehab-and-rescue-club-624452-236.html#post22034621
(There is also a link in the post to the "before" pics on the Authenticate This...thread.)
You will probably discover that the dark area on the front flap may improve with a bath, but will likely remain a little a darker. I'm a big fan of Leather CPR (try Tuesday Morning if you have one...much cheaper than Bed Bath and Beyond, at least in Florida!) and I apply it generously when the bag is still a little damp. Depending on how the bag feels after the first application, I may repeat it the next day. Then after another "day of rest" I finish with Blackrocks (read the product labels for directions for use), and usually buff with a brush.
I wish you good luck with your first rehab...and hope you find it as rewarding (and addicting) as the rest of us here. Keep reading and asking questions... we're all here to help!