My dog's black nails are turning clear. Should I be concerned?

Trauma to the nail, infection or even certain endocrine disorders can cause the nail color to change, but you would see other symptoms such as excessive licking of the paw, sensitivity, lameness, discharge, bleeding, swelling, weight gain or an increase in thirst or urination.
As long as Montgomery is behaving normally otherwise, there is likely no cause for concern regarding the change in nail color.