Female/male parakeets?

I have four parakeets. Two are rare parakeets. One is yellow and the other is white and blue. The other two parakeets are green and blue parakeets. There are the same color as their name. I have not named them yet because I don't know of they are males or females.

I need help with finding out either the birds are males or females. They are still not man-handled yet, but I am working with them. Can anyone give me any tips on how to see if the are males or females????? Plz