Are they supposed to do that?
I haven’t noticed this on mine, but some flowers do fade/change color to green as they age.
Are you growing a variety typically found in this solar system?
Are the petal turning green or have the petals fallen off and the teeny baby strawberries growing in the center of what was the flower?
The petals seem to be turning from white to green. They haven’t fallen off. There seem to me teensy strawberry-shaped clumps of greenness in the middle.
I really shouldn’t be laughing at this, but gosh darnit, you’re just so cute! 
Those are baby strawberries. Like the green bit in the middle of these flowers, right? http://www.digginfood.com/wp-content/uploads/2008/05/stawberryflowers.jpg The petals will dry up and fall off as the strawberry grows from the middle.
Heh. I knew that the tiny clumps of greenness are baby strawberries (though I haven’t grown any since the '80s when I was at home). Maybe the petals ‘turning green’ are just the petals drying out, and they look green because they’re reflecting the light from the leaves.