[halisaurus]

It's alluded to in the article that outdoor fields and green jerseys are the hardest. For outdoor fields the lighting is affected by the time of day, cloud coverage, players moving along the field, and plenty of other things I'm sure. It says they spent a lot of time creating a unique palette for the fields and that domed stadiums were preferred by the engineers on site. Indoor lighting probably reduced the shadows a lot.

[baddox]

I wonder if they use any tracking technology that looks at large groups of pixels over time. If you could track a player as a closed shape moving through space, you could mask out that player from the background even if pixels on the player's uniform were identical in color to the field's palette.