Why would a female mallard have a green head?

Hi everyone :) There is a mallard coming around my yard and swimming in my pool in the backyard. I noticed she was a mallard. So I looked up "female mallard ducks" on google and I saw, well they don't have green heads! I can now pet her and I have really have got attached to her :) she comes around alot but I let her go walk around, she always returns :) In the sun I can see she has a tinge of green on her head! I was thinking she had some "male mallard" in her too? But I thought that wasn't possible. Please help me! Thank you to everyone who helps me !! :D