It would make sense that their vision is less color sensitive because they are nocturnal. Rods, the photoreceptors that sense black and white scales, are more efficient than cones, the photoreceptors that sense color, in low light environments. It's why you can tell that a car is blue in the daylight, but you can't tell if it's blue or green if you see it going by at night. You can only see that it's dark or light.