I have used 'drone deploy' software to fly an area in nadir with a Phantom 3 advanced. The attached 3 photos show a series of frames taken within a few seconds of each other.

Does anybody have an idea why the middle photo is showing up in sepia colour? Several flight lines went over this area of ground, and a number of photos show the sepia colour just in this area.

When the photo mosaic is produced (1200 pics) it shows up as a 'tea stain' in one area of the orthophoto.

Try turning off auto white balance in the photo settings. Pick a value suited to the time of day.

The kelvin is too warm in the WB setting - set it 'sunny' to cool the image.

It's yellow rather than sepia and if you get images that are too yellow or too blue, a problem with the white balance is the cause.