The only tweaks I have applied were with TweakMB to double the amount of ammo in every commonly used ammo type. Throwing weapons like jarids, javelins, broad headed spears, arrows and bolts. And I reinstalled the mod and your single file to have a "clean" start.
I can see the standard heraldic colours on the other armours like the heraldic tabard, but the heraldic plate harness and heraldic plate armour remain white.
Edit: Okay, I'll specify, because I found out something quirky. I switched my banner from the yellow bird of prey on the black background to the red-white-red banner with the red rose. The plate -harness- suddenly displays the banner correctly, the plate -armour- remains white. I hope this confuses the issue sufficiently.
Edit 2: I think I may have found a source of the glitch. I started my character without a banner. Before I got one, I bought the heraldic plate armour. Then, I joined a kingdom, earned a banner and the armour remained white. However, when I found a plate harness, it showed the proper heraldic colours. Then, to test this, I prevented getting a banner until I could locate a heraldic plate harness again, -then- joined a kingdom in vassallage to earn the banner and unexpectedly.. -both- armours remained white. Finally, I started a new character, with noble background to have a banner right off the bat. I imported my rich template and hunted down heraldic plate armours and harnesses. Both suddenly had the proper colours!
I conclude that the armour must be loading its heraldic texture once in a savegame, and if you have none, it remains blank, or white. If you gain a banner afterwards, it won't update this. By comparison, heraldic tabards correctly show up as black and yellow chequered in merchants, and give you a black and red chequered appearance if you have no banner, while the heraldic plates remain white in both the merchant window and on the character.