Its all in this panels really:
http://www.batoto.net/read/_/94896/one-piece_v63_ch622_by_mangarule/5
when the border color becomes gray, that means its a flashback within a flashback. When it returns black, it means this is the present time of the flashback.
http://www.batoto.net/read/_/94896/one-piece_v63_ch622_by_mangarule/5
Here, Neptune says that Fisher tiger did it. Did what? To save the slaves. Borders becomes gray and he remember his talk with him:
"you mean to free the slaves?"
next page:
http://www.batoto.net/read/_/94896/one-piece_v63_ch622_by_mangarule/6
All borders are gray, its still a flashback within a flashback. Otohime can see that Fisher tiger has been a slave, but he still haven't saved anyone in Marijoa. He is about to.
And then the borders becomes black, we are back to the present time of the flashback after the attacks on marijoa. At this point, Fisher Tiger saved the slaves and they are worrying about the Reverie.
Cant make it more clear.