Teacore is brown vegetable tanned leather with a black topcoat sprayed onto it (pigment dyed).
The term came before FW, RM etc did all those artificial colouring, dyeing to mimic vintage leather and to speed up the fading.
You are very correct in pointing out that they artificially accentuate those contrasting wear by dying the leather in say brown then black. The photo posted describes not 茶芯 but 赤茶芯 a reddish brown core. 赤 means red in there. This is what some of those companies are going for in stead of the true teacore, a yellowish brown colour of raw tanned hide.
The term came to be known probably owing to the Japanese obsession about fading and aging of vintage clothing be it leather, jeans even nylon jackets. They also have a term "日焼" for the fading of nylon flight jackets due to extensive exposure to sunlight.
John Lofgren Monkey Boots Shinki Horsebuttt - $1,136 The classic monkey boot silhouette in an incredibly rich Shinki russet horse leather. 
Grant Stone Diesel Boot Dark Olive Chromexcel - $395 Goodyear welted, Horween Chromexcel, classic good looks. 
Schott 568 Vandals Jacket - $1,250 The classic Perfecto motorcycle jacket, in a very special limited-edition Schott double rider style.
That I think is a question for them to answer. One thing I have heard but not certain is that the fading is sort of a diary, a record of the life of the item as well as the wearer.
Obviously no expert. But two things I know. Things that fade and show wear are a sign of craftsmanship aka made well, longevity. Jeans or jackets don’t really fade or change if they are cheap. They eventually just break, or get replaced. Fades and patina show that it’s old and been around. Second thing I can think of, is that after WW2 with heavy American military presence on the island they inherited a lot of American hand me downs. Old jeans and jackets. New styles they hadn’t seen before. Americans outgrew them, bought new ones, styles changed and Japan took them all. So there was a generation or two, who grew up steeped in Americana of the 40s-60s. We also brought our movies and music with us that fed into this. Back then made in America really was a sign of quality and longevity. So the huge culture/society aspect of, then also the quality aspect. But what’s funny now is that a lot of the stuff being made which prematurely fades isn’t an exceptionally long lasting, well made product. Still well made for sure, some of the best, but some of the things being made teacore won’t even last a few months before they fade. I’ve seen some boots and jackets that are like 6 months old and look 30 years old. You’re losing the story the products tell, and losing the Mark of a product meant to last a lifetime. I think most teacore looks great and own a pair of teacore boots but the stuff that fades super quickly isn’t for me.
I think we have gone off topic but let me share my view which is
I wouldn't say I am a purist. I guess you can give it a new definition or that you may say it has evolved here but at least the Japanese would not understand it because to them the word means a particular colour. People use a literal translation of the term and lost part of its meaning. For example this D black J-100 is listed as "黒芯" black core.
I didn’t mean it was bad by any means. Just I don’t like pre-distressed or super fast fading. Some look good and look ok. Like Thedis wash he uses, love how that comes out. But in any case didn’t mean to sound like I don’t appreciate it, or think it shouldn’t exist. Just a personal preference thing. Not big on pre-distressed or the really really fast fades.
They write:
