Need more information on a Yellow Lady Gouldian Finch?

I purchased a Gouldian from an ad in the paper today, which had a yellow gouldian advertised for $40. I am pretty sure that is a good deal so I purchased it without too many questions, however it is lacking the red head I have typically seen in others. It is all yellow except for it's head, chest, and tail which are white. My questions are, what is this mutation called, how can I tell if it is male or female, and what would I get for babies if I bred it with a normal red headed bird?