Sounds like the cameras Infrared LED's are not illuminating the area. You can test this by having someone at the recorder viewing the live feed while its dark outside and having a flashlight then illuminate your area if they see it properly. If you can see then I would check if the camera has an OSD if so check if the Camera is set to be in color this would prevent the IR's from turning on if not  I would say the IR LED's need replacing if possible if not a new camera is needed. What is your camera model?