D5200 Color levels change through video Im shooting video using nikon D5200, just a man speaking in a green background.

The problem is that at the beginning of video the man is more "blue-ish" and as video progresses he becomes more "red-ish".

I noticed this at post-processing while trying to fix color levels.

What happened? Is this a constant auto-balance of colors from the camera while shooting video? How can i disable this and have the same color balance through all the video?
Don't use auto white balance and use manual exposure.

Auto white balance will guess at what is white and may shift while you are running video on some cameras (which makes sense since often people may move from one room to another while shooting or lighting conditions could change.

Manual exposure will preserve luminosity.  Auto exposure shouldn't change color temperature (which is what you are noticing) however it will change how bright things are and that can be just as much of an issue for trying to get accurate green screen footage.