Dogs, Cats, Horses, and Cows all have tapetums. This is a cat's retina, the tapetum is yellow. Inflamed eyes may appear red. A pet may rub or scratch their eye when inflammation is present. If painful, animals may also squint.
Rods are for sensing motion and work best in low light levels.
All mammals, including people, have more rods than cones. Cone cells are adapted for seeing in brighter light and can detect different colors of light. Humans have three types of cones. Dogs have two types of cones. Evidence suggests that the dog has vision similar to a human who is red-green color blind.