well, it's from the blue sky 'shining' onto your model... but it could stand improvement.
It is recommended to get rid of this quickly and easily in post-pro by using the white point feature in your image editor... takes only a few seconds
Choose pull-down menu in Photoshop, for instance, Image>Adjustments>Levels then choose the "white" eyedropper and click a point on a surface in the scene that is supposed to be white.
But another tip for users of Photoshop (or perhaps Gimp?), that works very nice and perhaps other editors have this features as well, is to use a photo filter to eliminate it in about 5 seconds.
This author set up an automatic action in Photoshop so that it can be done instantaneously at the press of the play button.
Create a photo filter layer over the top of your image as shown below.
- Use Warming Filter
- Set the color to RGB 100,100,80
- Set the layer opacity between 35 and 50 depending on how strong of a blue removal you desire.
- Couple this with using the recommended sky template here, and your blues will be gone in no time.