It is believed that nocturnal animals have little or no colour vision, but that all other animals have some colour vision. Scientists have determined that most marsupials, for example, have good colour vision.
Because animals have different ratios of "rods" and "cones" in their eyes, they have different levels of being able to see colour. Rods assist in seeing in the dark; cones assist with colour vision. The ratio of rods to cones in their eyes, as well as the type of cones themselves determines how much colour vision animals have. There are three types of cones which are responsible for colour vision, and each one has a separate pigment which is sensitive to red, blue or green light. What we may see in colour may be very muted colours - almost shades of grey - to dogs. But it is still colour.