I had a hippie wedding on the beach..even the minister was barefoot...sigh. Tie-dye is not from the hippie era, btw, it was later.
As for patterns, I'd go with something very optical. Central Park is a great free one from Timeless Treasures, and would look fantastic in your colors.
http://www.hancocks-paducah.com/Item--i-TT-CENTRAL-QP Or there are several purely op art patterns as well.