Consider, however, that "ye" is simply the archaic nominative form of "you" (where "you" is the accusative.) I would agree that "what think ye" is explicitly plural (to those modern speakers who understand the archaic) - but that a modern speaker would have no way of expressing "I say unto you" as explicitly plural without a circumlocution.
It was actually created as an archaic form to be used in poetry and translation of old texts, such as the First Testament, not in ordinary speech.
So no, it did not "disappear", it is still there for its intended purpose (familiar, btw, in no way unfriendly: You use it in the Lord's prayer).
Plus, in the real world, it is pretty rare that the person or persons you're talking to don't know it, and rarer still you don't know who you're talking to (probably the reason why English manages perfectly the way it is —that coming from someone whose native language does the singular/plural informal distinction).
I'm not sure it's 100% correct to say that it was created for this or that reason. You're right that it did not disappear. It was never part of the language.
Don't quote me, but my first guess is that "ci" was created because a few speakers wanted it and proposed it to reflect something in their native (modern) language -- but it was never used, not even in the Old Testament.
Question: Is "kolorblinda" an Americanism/Anglicism forced into Esperanto, just like "ludi (instrumenton)"? What I mean is: French: Daltonie, Spanish: Daltonico, Italian: Daltonico, Catalan: dàltonico, Portuguese: Daltônico, And Polish: Daltonista. Not to mention the fact that people with this vision impairment is not exactly blind to all colours. (protanopia, deuteranopia, tritanopia). I apologise beforehand if someone finds this question silly, odd or stupid.
On Android I can recommend Multiling Keyboard https://play.google.com/store/apps/details?id=kl.ime.oh
Kolorblinda is an adjective i believe and by themselves in esperanto you dont need to signify with an -n suffix because it is not acting on anything. The -n suffix signifies the object being acted upon in esperanto.
Viro mangxas hundo
Did the man eat the dog or did the dog eat the man?
Viro mangxas hundon...man eats dog
Viron mangxas hundo...the dog eats the man.
With kolorblindan you would use the -n if the kolorblinda is describing something being acted upon. Like if youre saying colorblind boy/man/girl/woman if the object word in esperanto is being acted upon by a subject word then yiu use the -n for both the object word and any adjectives attached that describe it.
Hope this helps. Kinda tired while writing so i hope it made sense and forgive my grammar.
In esperanto, for compound words, you add roots and only add the -o at the end if it is a name, -a if an adjective and so on. So, you take the roots kolor- and blind- to form kolorblind-, and to mean it's an adjective, you add the -a so that the final word would be "kolorblinda".
This works for every compound word in esperanto, that is, any word composed by two or more roots, as far as I know.