Had a few people IG interested in how I set up vtank to collect color armor pieces so this is my attempt to explain it here. This is how I have my Celdon, Yoroi, Covenant, Platemail rules set up... Unfortunately I've never had much luck with the Amuli rule so I'm not very good with that, though I never messed with it too much. I've also never attempted any of the new Olthoi Celdon/Amuli stuff so I'm not sure how you do that.
This is my covenant rule. A Yoroi or Platemail rule would be exactly the same just change 'Name' part to Yoroi.
Start by making a 'String Value Match' rule that Acts on 'Name' and then put 'Covenant' under String Value Pattern.
Now make a new rule inside this rule that is Requirement Type 'One Similar Color'. Enter the Hex # of the color you want to loot (you get this # by selecting an item in game with the color you want and typing /vt propertydump) In the screenshot below, the bottom line Ex Color C5C5C5 that is the part you want. Enter that number into the RGB color value (Hex) part
And then you can adjust the max diff hue. The lower the value the less different colors it picks up. However, I suggest keeping it ~5 because sometimes a pauldrons and girth aren't exactly the same #, so leaving some leniency allows it to pick up the different pieces that might be just a few #'s off but are actually the same color.
ALSO NOTE: Sometimes the exact same color pieces have different color #'s in vtank for some reason, I tend to just make multiple rules such as TevaWhite1, TevaWhite2 etc when I notice that. And on occasions vtank will be buggy and say an armor is color #000000 I have no idea how to fix that, I don't think you can.