Saints O revolves around WR, RB and one TE play...Outside of Colston their WR depth is Henderson, Meachem(FA), Arrington, Moore. With Colston and Meachem the primary outside targets for Brees, they can ill afford to lose both in FA.
I assume you are pointing this out because you're interested in Colston for the Pats? So I just want to point out that Colston is not at all an "outside target." In fact, he usually lines up in the slot and works the middle of the field (though much deeper than most slot WRs).