This is what worked for my mod.
public String getArmorTexture(ItemStack par1, Entity entity, int slot, int layer){
if (par1.itemID == Diamerald.Diameraldhelmet.itemID
|| par1.itemID == Diamerald.Diameraldplate.itemID
|| par1.itemID == Diamerald.Diameraldboots.itemID){
return
"diamerald:textures/models/armor/diamerald_layer_1.png";
}
if (par1.itemID == Diamerald.Diameraldlegs.itemID){
return
"diamerald:textures/models/armor/diamerald_layer_2.png";
}
return "diamerald:textures/models/armor/diamerald_layer_2.png";
}