I bet it\'s simply that they see in black and white in the dark, but can perceive colours at daylight.
Nightvision is usually described as an extra sensitiveness to infrared rays emitted by objects that have been warmed. Whether those creatures perceive infrared as white or a particular combination of colours doesn\'t really matter, since we can\'t describe the colors in infrared anyway as we can\'t see it. But I bet you\'ll be able to see the world in black and white at night when playing one of those creatures.
For those who skipped biology classes, we also got two kinds of receptors: cones for colours (more efficient at daylight) and retinal rods for black and white (more efficent at night).