Of course you want the best for your four-legged friend, but it can be hard to tell the good food from the bad. Generally speaking, dog food with artificial coloring is low quality. Most high-quality dog food manufacturer's don't feel the need to try and trick you with colorful gimmicks.
Purpose
Artificial coloring in dog food isn't put there for your dog's benefit. It's put there to appeal to the human buying the dog food. Brightly colored kibbles or pieces of food colored to look like vegetables or chunks of meat don't mean a thing to your pup. But they can lead a person to believe a food is healthier, tastier or full of ingredients that it doesn't really contain. Your dog doesn't really care what his food looks like. He just wants it to taste good.
Safety
In humans, artificial colors have been linked to allergies, behavioral problems and even cancer. Over the years the U.S. Food and Drug Administration has banned the use of many different colors in human foods. Even though the most dangerous artificial colors can no longer be used, some of those still used in both human and pet food, like Red No. 40, have been linked to cancer. Others can make your dog more vulnerable to viral illness. It is not proven that feeding your dog a kibble with artificial dye will cause him problems, and these foods are generally considered safe. However, it's smart to compare the risk against the benefit, and artificial coloring offers no benefit to your dog.
Considerations
The pet food industry is not regulated as much as the people food industry. Many things are added to dog food that would never be acceptable in human products. Labels like "natural" and "organic" are used rather loosely when it comes to dog food. Just because the package says it's natural doesn't mean that every ingredient is actually natural. When considering whether or not to give your dog a food that contains artificial coloring, consider the whole picture -- what else does the food contain? Consider the value of all the ingredients and choose the healthiest food you can afford.
Alternatives
Making your own dog food with lean cuts of meat and fresh vegetables is one way to avoid artificial coloring. But it's time-consuming and expensive. Many manufacturers of high-quality dog food don't add artificial dyes because of the risks they carry. The best dog food will usually be a natural brown or gray color, without anything added to appeal to the human eye. The focus instead is on nutrition. Many of these dog foods contain real meat and no byproducts or fillers. They are very healthy for your dog, but also expensive. There are also a number of manufacturers who have realized that consumers no longer want fake colors added to their dog's food. You can't always trust the advertising on the front of the bag, so check the ingredient list to find a food that doesn't contain artificial coloring.