Final answer:
Rods are the receptors in the eyes that are very light sensitive but only see gray. They are more sensitive than cones and responsible for vision in low light environments.
Step-by-step explanation:
The receptors in the eyes that are very light sensitive but only see gray are rods. Rods are more sensitive than cones and are responsible for vision in low light environments. They do not yield color information, so in a dark room, everything appears as a shade of gray.