They all work. I currently have A-Tom-Miks, Howies, Big Weenies, ITO's, Dreamweaver Action Flies and Siggs Riggs flies on the boat and they all catch fish.
As far as colors, If I had to limit myself to 4 colors of flies that will cover all water and light conditions, they would be Green Crinkle, Hammer, White Glow and Mirage. Others certainly work, but those 4 will always keep you in the game.
Tim