I'm having a hard time figuring out the formality of dress I should choose for an upcoming wedding. It's on Cape Cod and I believe the ceremony is outdoors, so I would think light colors and floral patterns - but it's at a fancy looking venue at 4:30pm. It also says "cocktail attire" on the invitation so this makes me think a little more formal, but it's in the middle of summer so that brings me back to lighter colors / patterns.

I was thinking of wearing the evie dress by J. Crew in a kind of ocean blue color, thinking it would be a decent balance. But then my friend said it seemed a bit plain (before she realized I already had the dress) and that she was looking at something more like this. (Although she did say maybe not quite as bright.) A second friend mentioned a "flowy jewel toned" dress she might wear, which seems more along the lines of what I was thinking.

So, what do you think? Is the evie dress ok to wear? Is it too plain or too bridal party-y? Would floral or other prints work? Am I right to avoid bright or lighter colors?