White color masking

Question
I have a blue eyed white male Persian. Is there a test to find out what color he is masking? In his past litters most of his white offspring have had a grey patch on the top of their heads. Does this mean that he is masking black? Thank you

Answer
I think you may have to consult with UC Davis about whether they have a test available which I'm not sure they do.  

The grey patch that his offspring display is common to most true white kittens and usually disappears by adulthood.

Regards

Marcia