Two pieces of armor with the same armor value, will provide the same protection, no matter the quality, level, etc of the item. Now, when you look at an armor you will see two numbers. The armor value and then in parenthesis the armor rating. The value is the one you want to look at. The rating just determines what the value is based on the type of armor. So light armor and medium armor with the same rating will have a different value (with the medium being higher).
As for orange armor, it's armor rating (and therefore armor value) is determined by the armoring modification. Whatever rating the armoring mod gives is the rating the armor will have.