Balhyocha is transliterated from Korean and means "fermented tea" or "oxidized tea"- the Korean language leads to this ambiguity. Hwang cha is transliterated from Korean and means "yellow tea". Hwang cha is always balhyo cha, but balhyo cha is not always hwang cha- this is important to understand. There are two categories used by Koreans to classify their tea: balhyo cha and bul balhyo cha, where bul means "not" (not fermented/oxidized tea). Bul bal hyo cha is exclusively green tea in Korea. Bal hyo cha is all the other Korean teas.
The production of Korean yellow tea was made famous by Jeong Yak Yong, a famous Cheoson Dynasty teamaster about 200 years ago. Yellow tea seemed to wane in popularity during much of the last century perhaps due to a resistance to Japanese occupation of Korea. The Japanese were primarily concerned with finding the perfect production area for another oxidized tea, a fully oxidized "Red tea" (Hong cha) or "Black tea" as it is called in England and most of the western world.
However, within the last few years Hwang cha has seen a dramatic rise in popularity. Hwang cha's recent popularity has spurred a bit of a shift in naming conventions. These days "Balhyo cha" seems to be more of the popular title for Hwang cha. The change of name preference and recent popularity reflects a growing health trend in Korea (and to a lesser extent worldwide) that appoints much health benefit to a regular diet of things "fermented/oxidized" (examples: Kimchi, yogurt, probiotics, etc).
It also reflects a general trend to more attention paid and more loose leaf tea being consumed by the average Korean, it is simply an option to the Korean who wants a change from green tea. Because it is very simple to produce, it offers a less expensive option to the expensive and labour intensive domestically produced green tea.
This blog uses "yellow tea" instead of "balhyo cha" simply beacause that is what ones first teamaster refered to it as. One is considering a change to "Balhyo cha"... the wonders of language!