Common /uncommon Uniques : why the same rarity name/colour ?

As I have read, there are 2 types of uniques: the common ones and the uncommon ones. I think I'm right when saying they have very separate drop rates, implying that looting infernal mantle does'nt mean that you could have had a shaveronne if the item had a different base.

And here comes my question: why have 2 rarity levels have the same name/color ?

I find it confusing that all the uniques are split in 2 groups and yet have the same color/rarity.
The probable cause I can see is that the devs don't want us to know if a specific unique is common or uncommon, but honestly it's often quite easy to guess:
- powerfull for all / best in slot = uncommon
- powerfull for very niche builds/ low level / useless = common

There might be exceptions, but are they worth keeping this confusing category ? Or maybe splitting it in two might raise the question "W

(if the issue has already been addressed, be kind and give me the link to the topic please, I'm feeling lazy)

You pretty much summed it up yourself pretty clearly.

Common = Low level, low-tier based Uniques that you would slap onto your newly created characters for a smoother leveling experience, only to discard them mid-late game.

Uncommon ones consists of Uniques that are optimal for builds mid-late game.

Why add two rarity levels with the same base type? Like the Occultist's Vestment?

- Simple, to screw you over and give you a mini-heart attack, and then make a thread on the forums QQing about RNG.

I think poeple would get less mad if there was 2 categories, let's say

Unique= common
Legendary = uncommon

Seems more consistent with the rest of the items categorization and less confusing.