Here's what gets me. Considering these sorts of fields are synthetic anyway, would it perhaps make more sense to actually have the field itself pre-colored at the plant? They could install the field in jigsaw like fashion, the colors wouldn't run, then they could probably recycle or donate the patches once the game is over.
I think that's what they do at MetLife, because the end zones always look like they're full of barely noticeable squares, while the rest of the field stays static.
Then again, painting is probably more cost effective, but whatever paint they're using, it does not bond well at all with artificial turf.