I think
Red is attack during defense
Blue means defend during attack

Why use red when you are attacking or blue when defending? Does red then mean attack while attacking??? Or defend while defending???

I play in normal mode and always have my two central dc in blue.... No more nose bleds for them by going high up, no more goals for them, less goals being conceded. Seems to work for me......now I only play 3 central at the back with dmc, even with ml, mr aml, amr by opposition.