I can only guess they inherited the 'PEW' half of their dad's genotype then, which was really a black or choc tan underneath. If they had inherited the himalayan gene from dad they would have been fawn or black, depending on which gene they inherited from mum. Do you know anything more about the himi line? Even if you do it may not reveal the black or choc tan part but we can only assume from the babies that it's in there!