Yes they can! Dogs have two colour sensitive cells in their eyes called cones. While dogs have a limited range they are able to see the primary colours of yellowish-green and blue-violet as well as shades of grey. From these they are able to make out a variety of colours but due to the fact they do not have the yellow cone (which we humans have), they are unable to differentiate between orange from red and orange from yellow. A dog visiting a park would see greyish green when looking at the grass or leaves on a tree. Flowers of red and yellow would look the same. To our dog we appear in shades of grey unless of course we are wearing yellow or blue clothing.
What does this lack of colour mean for dog owners and trainers? Using visual cues involving red and orange are best avoided in training. A lack of colour does not appear to matter to dogs as they are able to use other indicators to identify objects around them, in particular their superior sense of smell. We can help them by using the two main dog friendly colours yellow and blue in training including weaving poles, jumps and tunnels. Another area are dog toys or even using a blue or yellow mat or bed when training the dog to go to that spot. It looks like yellow tennis balls are the go!