Do you think it'd look bad if...?

I was wondering about what the groomsmen should wear. First off this is mine and my fiance's second wedding. So we want something fun and different. We found this amazin for the ceremony outside that has this beautiful little stream (bout ankle deep) and two islands with a bridge connecting them. We thought we would have my family on one island his on the other and get married in the water (walk out in between the two islands with our wedding party and stand in the water). My dress is just above my ankles and the bridesmaids are a little shorter than that we are wearing fancy sandals and taking them off at the edge of the water and going to carry them with the flowers into the water with us. Now my question is with the groomsmen and my fiance. The wedding is in the middle of june next year we can't decide if we want them to wear a tux or not. I'm guessing it'll be hot out and my fiance wants the guys to wear black shirts with bright pink and orange ties (our colors are hot pink bright orange with lime green as an accent color). But he also likes the look of the vest so here is my question. Which would look better having them rent the tux and just skip the jacket but wear the pants (rolled up while we're in the water) with the black shirt and colored tie and vest or have them wear black dress pants with a black shirt and just the tie? We just don't want it to look too formal for the feel of the whole thing, it's going to be a big wedding we just don't want it to be traditional we want something more laid back. Anyways sorry bout the babble just thought you'd need to get the "feel" of the wedding before answering.