https://www.yahoo.com/tv/s/nfl-address- ... --spt.html
I am not color blind, but this is an interesting concern. We take seeing everything in color for granted, but it's real. This article is long, but the chart at the top is illustrative of how someone who is color blind sees colors.
https://en.wikipedia.org/wiki/Color_blindness
Another thing, the players themselves. Even if NOT color blind, wouldn't it be easier for them to discern the opposite players etc with light or dark jerseys? You've got light variances regarding sunlight, shadows, whatever. We the spectators see it mostly on TV, with good viewing, but the players are in the heat of the action on the field, everything is moving quite fast, and your instincts are important down there.