along with the diamond shapes (male markings), that specific u shape colar mark is male. females may have fuzzyish (clouded) white patches or a crisp all white band (pied) in the neck region. another tell tale sign is that it is male, which really sticks out to me, is a striped or large dotted black (port hole) pattern that runs down the middle of the back to the tail. All that pretty white is covering it up on your little one, but if you look, it is there, especially on the tail.
scott