AFAIK only clothing can be owned, but not metal armor (or leather armor / leggings, for that matter). Dwarves can grow attached to armor pieces, shields and weapons though, but I don't believe that would cause the equipment listing entry to turn red.
If they are red in your equip list, check the stocks screen as well. Does there happen to be a yellow letter F, a purple letter D or a red letter M next to it's listing there?
nope they are not any of those, or in brackets for forbidden.
I have played with the raws to prevent particular animals from appearing, (simply removed them) and that has worked. I am also cheating a lot on this save with changing all my items to masterwork steel
So perhaps DFHack has made a mess of it?
i am 99% sure it's to do with changing "over clothing" to "replace" clothing after changing which squad a dwarf is in. For example, i just changed one dwarf from one military to another, as i'm hoping my legendaries will possibly consider sparring with him, or that he'll learn somewhat faster. I noticed he took off all his items, and proceeded to pick up new ones, my entire equipment list for some armor types is red (excluding clothes). So my guess is that all that he was wearing, is now highlighted red and now the second set he has on, is also red.
i mean it in this screen:
as you can see, all of it is in red except the artifact. I actually have some which arn't red for boots, but that explains why he put 2 shoes on without a problem. But as a good example, i have literally 40 shields sitting next to him, instead he picks up a recently killed goblin one which is copper, i'm pretty sure they replace items to the best possible, so there is something weird going on.