Avian biotech online can DNA sex for $19.50 per bird, but i'm not good at telling the sex.
I have a parakeet with the blue and yellow head also. I was told its an easter mutation but I dont know if thats even a correct term. They look adorable!
The blue one looks like a girl and the yellow one looks like a boy I think I cant tell on the yellow one. They both look about 4 months old. The bars on her head are half way and the yellow ones eyes have a little color in it, those both indicate that they are about 4 months old or so. They are very cute! I love the yellow one!
I believe the males have a blue nare, while females have brown. are they young? If so they may still be developing the color. The bird with red eyes(lutino) probably can't be sexed by the nare.
The blue one is definitely a female for sure and the Lutino I believe is a female as well. The blue one is older then 4 months! If you don't have a lot of knowledge on birds right now, I would not suggest on breeding at the moment! Once the females are sexually mature their cere will turn crusty brown. But lose them when they're not in breeding mode.