When going to search a dog, a list or breeds/sex/for stud ect comes up, I think their should be a option where you check off (or click) the markings you want the resulting search dogs to show up with, you can press CRTL and select more then one also (as seen on mweor another sim site I've used)
This way if your looking for a corgi with Piebald for stud, you fill in the option of "for stud, corgi" and then select "piebald" off the marking chart for that breed and if there are any dogs with that marking (or combination) the results will show them.

Good or bad idea? What do you think?