The dark armour is plate with a fixed gorget. So this would date the armour to the 15th Century.
Actually darker armour would be more historically accurate on used armour. Often armour was left black from the forge to protect it from rust as well as it was painted (again to protect it from rust - just like we do today with our cars).
Anyway, I like the dark armour. I think it gives a good contrast with the "silver" of the legs (which would be Playmobil's version of chain mail).