So it's actually false that at nighttime, he shouldn't be able to see. We have two photoreceptors in the retina: rods and cones. Cones are used when there's lots of light and help us perceive color. Rods are used for acuity in darker settings. So when nighttime comes around, we actually don't use cones much and rely heavily on rods to see better. In other words, in dark settings, our ability to perceive color is shit and almost everyone is incapable of seeing accurate colors. BECAUSE he can't see color, the prince would be using his rods more and therefore, be able to see at night better, probably better than the average person to be honest. Just because he can't see color doesn't mean he shouldn't be able to see at all.
So it's actually false that at nighttime, he shouldn't be able to see. We have two photoreceptors in the retina: rods and cones. Cones are used when there's lots of light and help us perceive color. Rods are used for acuity in darker settings. So when nighttime comes around, we actually don't use cones much and rely heavily on rods to see better. In other words, in dark settings, our ability to perceive color is shit and almost everyone is incapable of seeing accurate colors. BECAUSE he can't see color, the prince would be using his rods more and therefore, be able to see at night better, probably better than the average person to be honest. Just because he can't see color doesn't mean he shouldn't be able to see at all.