And immediately thought about accessibility testing in first few seconds.
Now consider if a player, linesperson or ultimately the referee happened to be colour blind, could have been chaos not just for the viewer.
Edit*** This will seem very random as I could not add a picture. Both Newcastle and Sunderland played in their home strips, this does not happen in league games but was allowed due to being an fa cup game.
I was confused at why you brought up the topic at first! 
I found an article on the topic of the colourblind issue with Sunderland v Newscastle kit clash.
I turned the image black + white, which might not be entirely accurate, but is probably a good representation of what colour blind people see.
To be honest - it was the first thing that crossed my mind!
Glad this has got some publicity, maybe the FA should take note. I am sure some players have been affected by this - But imagine they were on the Sunderland side based on the result 
