So? Why Dogs Muzzles Turn White? 

Just like us this change normally related to aging but there can be other factors to consider. Notice I'm hiding my own greying beard in the pic, sorry Khaleesi, this ones on you!

Age-Related Greying

Just like us humans, dogs can show signs of aging through greying hair.

For most dogs, the first signs of aging hair will appear around the muzzle and can happen as early as 5 years old.  The timing of this though can vary depending on the breed, size, and individual genetics of the dog. Khaleesi is my youngest of 4 and is the only one to show this trait. Larger breeds also are more likely to show signs of aging earlier than smaller breeds.

Genetic Factors

Some dogs may start to show white or grey fur around their muzzle earlier than others because of their genetic makeup

Health Factors

Although this is normal part of ageing, if your dog's muzzle turns white prematurely or rapidly, it could potentially be a sign of stress or health issues. If you have any concerns about the rate or pattern of greying, I'd recommend consulting your vet.

The greying of the muzzle isn't normally something to worry about and is a natural sign of ageing but if accompanied by other symptoms or changes in behaviour then it's important to seek additional information from your vet in the first instance.