Are you aware that breeding two birds of the same mutation together produces inferior birds? It is best to keep the two you have and find birds that are split for the mutation you want.
This will keep the undesireable traits down to a minimum and keep the health of the birds up.
In breeding of gouldians, no reputible breeder will breed two birds that are white breasted toghether, this also goes for the blue mutations and the yellows as well. People who do these things end up with smaller birds, and in the case of the blues, ones that cannot absorb vitamins correctly.
When breeders of cockatiels bred lutino mutations together, they ended up creating the lutino bald spots that tiels are plagued with. Only with careful breeding can we preserve the genetic stock that we currently have. Why risk putting more birds out there that could carry a genetic defect that can easily be prevented by breeding in a more careful manner?
Try reading this site
http://www.multiscope.com/hotspot/genetics.htm They can help you pair your birds correctly for healthy offspring that will carry the traits you desire.