[casinobonuscxz]

From different sources from a google search:
'The blue roofs were popular aesthetically for a short period in the 1970s, but you don't see new buildings these days with blue roofs. Most now are grey, but there are some that are orange.'

"blue roofs... during the Joseon dynasty a blue roof denoted royalty. Now it's just for show."

'As part of an effort to modernize Korea, the late President Park Chung Hee enforced the so-called "New Village Movement" (Saemaeul Undong in Korean) in the 1970s, aimed at developing agricultural villages. In 1971, 335 sacks of cement were offered to 33,267 rural towns, and used for transforming the tradition-bound straw-thatched houses [choga-jip] into roofing tiles. So the tile roofs of the most houses were produced during the nearly same period. Thus we can guess that "entire villages came to have new roofs" with certain designated and stereotyped colors. When it comes to colors, we have to take into account the Korean people's color sense in architecture. On the basis of theory of five elements [o-haeng]and yin and yang as well as the traditional Korean colors of obang-saek (five colors of red, blue, yellow, white and black) has been widely used and among those, red and blue have been the main colors. (Think of Korean temples decorated with splendid, primary colors, mostly red and blue). Of these colors, black and white, widely loved by Koreans since old times, were not appropriate for colors to arouse people's will to modernize their town. Also there is a view that in order to make the "New Village Movement" visually prominent, the ex-President Park might have wanted the roofs to have bright colors, particularly for the houses located along the highways.'