Personally, I think both of the dresses in the links are gorgeous and would be appropriate. The seafoam green one is a similar style to the dress I'm wearing for pref night (except it's black).
Now I am also a pnm so my advice may not be as helpful to you, however, I do know a few greek women at Texas State and they have told me that the greek system there is much more relaxed than it is at most schools in Texas. This could mean that any color dress would be fine. Again, I am only a pnm and do not know for sure, but I think the fact that the whole system is more relaxed should be a hint to how rush is going to work.
Good luck