I am not so sure it really works. Even though the colors may correlate to coat colors, different colors can be obtained from the same dog in different angles. Here is a quote and link to check out:
"When you take photos of animals, the red eye effect can be quite different. Animals have a reflective layer in the back of their eyes behind the retina called the tapetum. This layer enhances their night vision. The colour of the tapetum gives you blue, green, yellow, or white eye effect. With animals, the effect can have place even when the ambient light is sufficient to prevent it in humans. ... Tapetal color can vary to some extent with coat colour. Some animals, and a few dog and cat breeds (for instance, blue point siamese cats), have no tapetal pigmentation. These animals show a red reflex as humans.
The color of the eyes in the picture also depends on the angle at which you take a photo. Taking pictures of the same animal from different positions of your camera may produce different results: "(Take a look at the site and you will see they get different color eyes from the same dog in different angles!)
http://www.colorpilot.com/redeye_effect.html