Identifying white canary

[fredbernie]

I've just acquired a pair of white canary. I know it is not an absolutely good idea to breed two white canaries, but it is not easy to find a good yellow sample in my place and a blue is not my option so I went for two white with the hope that one is dominant white and the other is recessive white. Now I am pretty sure that the female is recessive white as there is no yellow patch or black feathers whatsoever on her body. She is of 2014 and is slowly coming into condition. The male has finished the molt and start singing hard. However, I cannot tell exactly whether he is recessive or dominant. He is all white without any yellow tinge, except for an area on the back of his head which has a patch of black feather the size of the thumb tip. It is not pure black, just scattered feathers but can be distinctively recognized. So folks, please give me an idea what he might be. I think he is dominant, but I'm not sure.