At what age will JTR markings stop forming?

by Cindy
(Parker, Colorado)

Ellie and her pinky pal

My husband rescued a young female JRT from a puppy mill raid. We don't know how old she is, but within 5 months of acquiring her, she began to develop further markings. When we adopted her she was 90% white with a tan mask around both eyes and ears. And the vet estimated that she was a year old. Now we are noticing the development of black markings on her belly, legs and two small markings on her back. The belly and leg markings do not have black hair but the two small markings on her back have turned to black hair. At what age will the markings stop forming?