https://deadspin.com/heres-why-nbc-introduced-the-green-zone-which-maybe-1828627651

This season, the No. 1 program on TV is introducing a new feature that digitally turns the field a slightly darker shade of green during third downs to show the distance between the line of scrimmage and the line to reach a first down. Executive producer Fred Gaudelli calls it an "evolution" or "complement" to the yellow digital line that was first introduced 20 years ago.

NBC's new Sunday Night Football "Green Zone" is the ultimate conclusion of graphics creep (https://www.theringer.com/nfl/2018/9/6/17830436/nbc-green-zone-eagles-falcons-first-down)
NBC's new graphic, which puts a green zone between the line of scrimmage and the first down line on third downs, made its formal debut on Thursday night to the distaste of many viewers. "Viewed positively, the Green Zone alerts fans to the fact that it’s third down," says Rodger Sherman. "Viewed negatively, the Green Zone does absolutely nothing besides tell the audience it’s too stupid to identify the first-down marker with just one on-screen graphic."