What other color goes great with Ocean Blue, besides Green?

My sister is having a sweet 16 and her theme is "Under The Sea". So far we've got her mermaid-style dress which is going to be a sort of deep ocean blue. The problem is is that she has a court consisting of 7 couples and she doesn't know what color(s) the girls and guys should wear that can look good with her dress color. I know a green would be good but my sweet 15 was blue and green so she doesnt want the colors repeated. What would look great with an ocean blue???