Red arrows will motivate a player to be more attacking (players have 2 skill sets Defensive and attacking and can use either 1 at any time). So a red arrow will increase the chance of attacking choices. This extra motivation also uses more condition on average.

eg an ML with a red arrow will NOT become and AML (Nordeus don't give free extra roles ) but he will try to get forward more, play with greater physicality and choose attacking skills more.

Nordeus has given answers on this several times (3 I think) but sometimes used confusing language.

My personal way of thinking about it is in Orders the Mentality changes things at a global level, Arrows do it at an ingividual level.