Helping You Know if You Are Going to Be Getting a Pure White Pomeranian
Ethical, professional breeders will do their best to make educated guesses on the color of the Pom, however it is almost impossible for the breeder to know for sure what the adult color will be. However, as stated above, any shadings of other colors , especially behind the ears, is a good sign that the Pom will NOT be white.
It is best if you also:
Ask to see the sire and dam (parents) of the puppy. It is best to see the parents in person. Photos can be extremely misleading (or in cases of unethical breeders, they can be touched up with PhotoShop).
If a breeder has the ability to produce whites, they certainly should be able to show you, in person, some of their white dogs. If you are purchasing a puppy over the Internet, be aware that there is something amiss if you see white Pomeranian puppies on the site, but no adults of that color.