I would definitely wear boots! You want to wear a pair that you can walk the flats for a good part of the day, and that seal tight around the ankles to keep out sand. Nothing worse than sand rubbing your feet raw. Also, there can be stinging animals, coral, anemonies, small outcropping of rocks, etc. They should also have drain holes or fabric to quickly drain water.
Black boots should be ok, you're going to be standing in water that goes from ankle deep to knee deep so color is not a problem. I've also seen neoprene "socks" that you wear inside of flat boots. They fit tight around the ankles. I don't have any "socks" so I can't speak to their effectiveness.
Therefore, my suggestion is not to wear sandals.
I have a pair of flats boots that are made by a company called "bite", and I believe I bought those on line at Cabelas. They have worked great. Korkers used to make a pair also, and may still do so.
Feel free to ask more questions, it always helps.