What is the purpose of the colour-coding?
Counter question: Why does that bother you?
Would anything be different, if those items would have regular white tooltip, rather than green?

Yes indeed, the world would be a brighter, happier place without item colour-coding! I would not be spending my time trying to work out why the developers had included something in the UI that appears to have no purpose, which would lower the cognitive load on my poor addled brain, which is quite inportant as I am old and increasingly senile.
I'll assume that you misunderstood the meaning of the paragraph that you have selectively quoted, as English is not your native lnguage. That paragraph outlined how I generally would like items to appear ( to paraphrase myself; consistent and logical, unless created by a known loon).
The paragraph that followed...
Some of the BG3 items fail those tests, without apparently being created by a known lunatic.
...expressed my view of the current BG3 items.
and without illogical restrictions
This is just matter of point of view mostly ...
People keep complaining about "when you have 50% HP" items the most ...
I wouldnt say it translates to "you have to be half dead" ... after all, person with last 1HP is working in this game as just as healthy and capable of doing things as person having full HP, wich we are certainly not if we are single punch from beaing beaten to death ...
So you simply have to be wounded, wich is quite common condition in fantasy, in Dragon Age there is whole magic type based on spilled blood. O_o
Sure we can still ask who and why would create an Magic Armor that is powered by its own wearer blood ... but that is again just matter of poing of view.
Its creator could (just for example) see potential power in that spilled blood, and decided that if you are going to get hurt anyway, you could at least gain something of it, rather than just being harm without any use.
Or it could be failed experiment.
Or ongoing research, if that power of blood would actualy work.
Or it could ben sucesfull experiment, that didnt really catch with people.
Yes, of course it's point of view. Personal views are exactly what people are expressing in discussions like this; even if we sometimes like to pretend our views are objective fact, they are never really more than opinion and preference.
This particular example you cite ( an item activating only when you are injured ), fails my personal tests for a thoughtfully designed magic item; but I appreciate you, and other players may find them interesting. Dragon Age ( as you brought it up ) does indeed have "Blood Magic" for the mage and "Reaver" for the Warrior, where a benefit is exchanged for loss of personal health. The magic item equivalent of this would be, for example, a weapon that does additional damage to your target by drawing power from the wielder, probably in the form of health damage. Such a weapon, even without an interesting creation story, is consistent in it's behaviour, as well as being logical, so long as it inflicts more damage on the target than the wielder; so I would probably like such a weapon.
By contrast, in BG3 you can find magic items that I find very interesting, when someone has thoughfully designed them as part of the game world and story. The amulet you can obtain near the forge in the underdark stands out, but even the "Sword in the Stone" added to the underdark during EA, which was nothing more than a +1 longsword, was interesting because it had a story, and you don't get it just by clicking on a chest or dead body.
I mean, this is the same story as with the tadpole over again ... there is countless (resp. as much as you can make) ways to explain things ...
You just need to open your mind a little, rather than just repeating "you would need to be bad, crazy, stupid, or all that combined to ... w/e" ... but ofcourse if that is the only explanation you are willing to accept ... well, its quite sad story i would say. :-/
I can't really respond to this, as I don't have a clue what you are talking about. I don't recall ever contributing to any significant discussiom concerning the tadpole. To date, I have played through EA several times, doing everything from refusing all interaction with the tadpole at one extreme, through to accepting all interactions such that my status flips to "True Soul" at the other extreme. If the released game is good enough, I will probably play through the whole thing several times, playing with different character mind-sets; that is really why I like to play RPGs.