Yes, they can see color very well. Someone mentioned they can see depth, which is true, but they can't see depth very well. Depth is perceived by where the vision of each eye overlaps. Since a ducks eyes are on opposite sides of its head, it has a small area where it can perceive depth very well. Try covering one eye and estimating distance, its not easy. So, when you have a spread with decoys of all different sizes, a duck in the air cannot differentiate the size difference very well until he sits down next to them.

Instead, ducks have very good movement detection. This is why movement in a spread, such as a jerk cord or robo duck, draws their attention. It is also why they will see you bobbing around in the blind when they are overhead.