Before we are able to time travelling, no one could say, what colours have tunica, shields and so one.
Also the monuments shows only, what the artist like to show us..
Many historicans think, that also figures of the trajan column could be an order of the emperor to the artist.
Praetorian guard units may have the best of the best equipment, but it could also be, that the actual emperor would see them wear hoplite style armour elements, the next emperor would like to see his guard in combat armour, simple lorica segmentata, may be they have greaves, may be greek style, may be all in decoratet centurio style, may be plain steel, may be none?
Most details of the uniform and equipment is speculative.
I have discussed this with Adam many times and he decide to show us the praetorians in this way.
Better greaves than the normal legionary ones, manica and mail fists.
There are many manica foundings, and mail fist for special units is also logical, because an arm protection without hand armour is only half as good..
Romans know very well to do mail armour, why should they not do the final step?
In some books about the roman army of the middle imperial period, there are legionaries shown with this mail fists.
And yes, there is again no one you could definitive say yes they have worn this or not.
Adams idea is to show the roman army, from the theme equipment, at their best time period.
Only because some customers would like to see legionaries with older helmet types he sculpted some.
In the time of Marc Aurel, most legionaries may wear indeed the best and the last italic style helmet, the Niedermörmter helmet.
There are some differences between the uniform of the legionary of the dacian wars and this of the "Markomannenkriege"
After the Crisis of the Third Century and the later emperors (235–395), all have change, and the glory days have been only memories.
The problem is, that we know very few about this times and what we know, could also be a mix of truth and propaganda.
So I think, that every tabletop gamer and collector should do what he like, not important if the tunic is white, brown, blue, red or green.
Also no historican could tell us the truth.