First off your bird should be at least 6 months old before you will be able to really tell its sex. When i got my first female bird she had a really dark brown cere, but then it turned white, and now it has gone back to brown. All of my males have always had blue or blue-purpilish ceres the whole time I have had them.

Okay, first thing now is to look at the fleshy thing above the beak. Females will have a brown or tan cere. If the bird is Albino or Lutino the cere on the bird will probably be pink. Males have blue or a purpley-blue cere. Another thing you can do is watch for these behaviors. Males will probably sing and be more playful and willing to try stuff new. Females are usually really Bossy and Pushy among the other birds around her.

Here are some picture examples: Note: I am going to take some more pictures and put them on here as soon as possible.

Males:

Normal Blue Cere	Purple Cere (Recessive Pieds and Albinos/Lutinos)

Females:

Normal Brown Cere	Normal Tan Cere	Pale Blue / White Cere