A colorless discharge in a dog's nose (runny nose) is a common problem. Most of the time, a dog licks it away with its tongue. So, an owner may not notice it. Such discharge, if without symptoms, is not a cause of immediate worry. An owner should wait and see if the runny nose stops on its own or he/she should look for signs of illness of any kind. However, in case there are signs of discomfort or if the discharge is bloody, grayish, purulent, or viscous, then a visit to the vet is necessary.